U.S. patent application number 14/484432 was filed with the patent office on 2014-12-25 for process for the rapid fabrication of composite gas cylinders and related shapes.
The applicant listed for this patent is Pamela M. Schneider, Steven C. Stenard, Geoffrey Michael Wood. Invention is credited to Pamela M. Schneider, Steven C. Stenard, Geoffrey Michael Wood.
Application Number | 20140374950 14/484432 |
Document ID | / |
Family ID | 39885588 |
Filed Date | 2014-12-25 |
United States Patent
Application |
20140374950 |
Kind Code |
A1 |
Wood; Geoffrey Michael ; et
al. |
December 25, 2014 |
PROCESS FOR THE RAPID FABRICATION OF COMPOSITE GAS CYLINDERS AND
RELATED SHAPES
Abstract
A method of fabricating a composite vessel encompassing rapid
manufacturing. The process includes using a liner, of metal or
plastic materials, over which a braided or developed preform is
wrapped. The dry fiber wrapped liner is placed in a mold and resin
injected into the cavity formed between the liner and the mold
outer walls. The liner is flooded with heated and/or cooled
pressurized fluid thus enabling complete and independent process
control from within the liner for both the resin injection and the
cure phases. Fiber placement control is determined through combined
biaxial and triaxial braid/preform design, and by wrapping at
controlled tension onto the supporting liner. Fiber tension control
is further enhanced by the methodology of mold loading whereby
tensioning forces are enacted during actual load and close. The
process may use thermoset or thermoplastic resins and any of a
variety fibrous reinforcements.
Inventors: |
Wood; Geoffrey Michael;
(North Saanich, CA) ; Schneider; Pamela M.;
(Independence, KY) ; Stenard; Steven C.;
(Cincinnati, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wood; Geoffrey Michael
Schneider; Pamela M.
Stenard; Steven C. |
North Saanich
Independence
Cincinnati |
KY
OH |
CA
US
US |
|
|
Family ID: |
39885588 |
Appl. No.: |
14/484432 |
Filed: |
September 12, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12046716 |
Mar 12, 2008 |
8858857 |
|
|
14484432 |
|
|
|
|
60906282 |
Mar 12, 2007 |
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Current U.S.
Class: |
264/257 |
Current CPC
Class: |
B29L 2031/7172 20130101;
B29K 2101/12 20130101; F17C 1/005 20130101; B29C 35/0288 20130101;
B29C 2049/2008 20130101; B29L 2009/00 20130101; B29C 2049/2047
20130101; B65H 81/06 20130101; D04C 1/06 20130101; B29C 49/6409
20130101; B29L 2022/00 20130101; B29C 45/14786 20130101; B29C
70/443 20130101; B29C 49/20 20130101; B29C 35/045 20130101; B29K
2713/00 20130101; B29C 49/6472 20130101; B29L 2031/7156 20130101;
Y02E 60/32 20130101; B29C 70/446 20130101 |
Class at
Publication: |
264/257 |
International
Class: |
B29C 45/14 20060101
B29C045/14 |
Claims
1. A process of rapid manufacturing of a composite hollow article
comprising: providing a liner; applying a dry fiber over-wrap
around the liner; placing the liner with over-wrapped fiber into a
mold cavity corresponding to the outer shape of the composite
hollow article and providing a cavity between the liner and the
mold wall; delivering a fluid into the liner capable of heating or
cooling the liner; injecting resin into the cavity between the
liner and the mold wall to permeate the fiber over-wrap; removing
the composite hollow article from the mold cavity; and a) wherein
the liner is subsequently removed, or b) wherein the over-wrapped
fiber is in the form of a stitched fabric material, or woven fabric
material, or filament wound tow material, or c) wherein the resin
used for the composite is thermoplastic resin.
2. The process of claim 1 wherein the liner is subsequently removed
via melting.
3. The process of claim 1 wherein the liner is subsequently removed
via dissolution.
4. The process of claim 1 wherein the over-wrapped fiber is in the
form of a stitched or woven fabric material.
5. The process of claim 1 wherein the over-wrapped fiber is in the
form of a filament wound tow material.
6. The process of claim 4 wherein the fabric material is
constructed of bi-axial fibers.
7. The process of claim 4 wherein the fabric material is
constructed of tri-axial fibers.
8. The process of claim 4 wherein the fabric material is
constructed of a combination of bi-axial and tri-axial fibers.
9. The process of claim 1 wherein the resin used for the composite
is thermoplastic resin.
10. The process of claim 9 further comprising during the step of
injecting resin, controlling the temperature of the fluid inside
the liner during injection; and wherein the step of heating the
fluid comprises heating the fluid in the liner to a temperature
higher than the melt temperature of the resin.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 12/046,716, filed Mar. 12, 2008, which claims from the benefit
of Provisional Application Ser. No. 60/906,282, filed Mar. 12,
2007, both of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to the art of fabricating composite
hollow structures with internal liners; more particularly to
improved methods of manufacture of composite pressure vessels for
storage of hydrogen and natural gas, specifically with respect to
improvements focused towards high-rate manufacturing
methodology.
BACKGROUND OF THE INVENTION
[0003] The primary issues associated with implementation of fuel
cell vehicles and the like are in manufacturing components at rates
compatible with vehicle production, and at costs that can be borne
by the consumer and industry. Current high-pressure storage
cylinders need to be carbon composite due to the weight penalty
associated with metallic tanks. However, current state-of-the-art
in composite cylinder production relies on filament winding of
either wet fiber tows, or of a pre-preg fiber with pre-impregnated
resins (typically epoxy or possibly other thermoset and some
thermoplastic resins.) These are wound onto a liner with precise
control of fiber orientation to allow optimum stress fields, and
the overall wound cylinder is typically placed in an oven or
autoclave and cured for some period of time. The typical process
sequence can take from 4-8 hours per cylinder, and for example, as
referenced by lida et al (U.S. Pat. No. 6,190,481) a cure time of
over 6 hours was demonstrated for tank manufacture. The state of
the art is further reflected in patent literature such as
Goldsworthy et al (U.S. Pat. No. 6,565,793) and more recently Iida
et al (U.S. Pat. No. 7,032,769).
[0004] In order to be compatible with vehicle production rates, a
process that is approximately 20 minutes or less is desirable. In
the above referenced state-of-the-art, from 12 to 24 different
tools and process lines are necessary for the parallel processing
required to reach 20 minute product cycle times. This is capital,
labor, and space intensive, and is not optimum for real-world
production requirements. The current status has been verified by
recent private communication with a major automotive
manufacturer.
[0005] Attempts have been made to modify other composite processes
to take advantage of faster cycle time, including using resin
transfer molding into a dry-fiber preform which is filament wound
onto a cylinder liner. The issues with these approaches have come
from holding appropriate tension on the fibers after wrapping, with
holding net-shape on the carbon wrapped liner so that mold closure
does not wrinkle the carbon fibers and thus knock down the
properties to unacceptable levels, and with rapid and repeatable
injection processes. The latter is a key factor as the existing
systems have typically used heat and pressure transfer via the mold
external surface, and utilizing pressure control via injection
pressure of the resin.
SUMMARY OF THE INVENTION
[0006] The invention utilizes a formed liner which is over-wrapped
with a dry fiber fabric preform or braid. Tension control is
incorporated through use of a tri-axial form of material such that
tension can be developed in the preform without deformation. The
wrapped liner is loaded into a mold cavity defining the outer shape
of the part to be made. The loading operation incorporates rotation
of the liner and fiber preform such that the tension on the preform
is improved and is coordinated with tool closing to effectively
eliminate any undesirable possibility of wrinkling of the
preform.
[0007] The liner is connected to process controls capable of
delivering heat and cooling as well as pressure to the inside of
the liner via fluid systems. The capability to control the process
from the internal liner side is used during the subsequent resin
transfer molding operation. Resin is injected into the dry fiber
preform occupying the cavity between mold wall and liner. The
temperatures and pressures are capable of being set at optimum for
the injection cycle, with rapid thermal response from the liner
process fluid systems and pressure balance as provided by the liner
internal fluid preventing collapse of the liner. Additionally,
vibration and other pulse based injection process aids can be
accomplished through fluid excitation in the liner.
[0008] Once resin injection is completed at the conditions chosen
for resin viscosity and flow control, the liner internal fluid
system is switched to provide optimum thermal and pressure settings
for cure of the resin. In this manner, complete separation of the
resin viscosity profile for injection and for cure are attained,
and as evident to any practiced in the art, the overall process
cycle can be optimized. Additionally, the pressure conditions
developed in the resin can be selected for achieving properties
desirable in the final part. On final cure the part may be cooled
as desired via internal cooling through the liner, and thus the
demolding cycle can be accelerated as well.
DESCRIPTION OF THE DRAWINGS
[0009] A brief description of the drawings indicates the process
methodology developed herein.
[0010] The cylinder liner, fabricated with double-ended threaded
connections, is placed on a mandrel and a direct wrap of fiber is
applied, FIG. 1. In the first embodiment of the invention, a
braided carbon fiber material is used; however either stitched or
woven fabric forms may be used as long as the correct fiber
architecture can be accommodated.
[0011] In the first embodiment and as applicable to pressure
cylinders specifically, the braid is a combination of tri-axial
format and bi-axial format as shown in FIG. 2. The fiber
architecture required for achieving design properties can be
developed in this way. The bi-axial fibers conform to the end-dome
design and the use of longitudinal fibers allows tension to be held
in the fabric without distortion.
[0012] FIG. 3 shows an additional strip of bi-axial fibers stitched
onto the wide format braid to allow build-up of additional
thickness on the tank ends, as well as to mitigate the effect of
changing thickness of the fabric where the uni-directional fibers
stop.
[0013] FIG. 4 shows one embodied method of drawing the braid down
to the tank ends and using a pick system.
[0014] FIG. 5 shows the schematic for achieving process control
over thermal and pressure conditions from the liner outwards during
the resin injection and cure process.
[0015] FIG. 6 shows the method of tool load and tension control
during the mold closing operation.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0016] The following discussion of the embodiments of the invention
directed to a rapid manufacturing process for a compressed hydrogen
tank is merely exemplary in nature, and is in no way intended to
limit the invention or its applications or uses. However, as will
be appreciated by those skilled in the art, the process has
application to produce tanks other than compressed hydrogen tanks
and to produce structures with liners applicable in a number of
fields utilizing composites as the preferred material.
[0017] An invention is developed which consists of several process
steps, intricately linked, in which no single step is more than
10-20 minutes in total cycle time, thereby resulting in a part
fully completed coming off each line every 10-20 minutes.
[0018] A cylinder liner 1 is formed through one of several options,
using either superplastic forming of metal pipe with threaded ends,
spin forming of cylinders from metal sheet or tubing, or plastic
blow-molding or injection molding to form plastic liners. In the
case of using plastic liners, an additive may preferably be used to
allow higher thermal conductivity than with current plastic
systems, and these additives, which are well known in the industry
and include nano-particulates of conductive materials, or chain
forming additives to preferentially conduct heat. Plastic
formulations are incorporated herein that include carbon nanotube
modified plastics that have high thermal conductivities as compared
to un-modified materials.
[0019] The cylinder liner 1, fabricated with double-ended threaded
connections 2, is then placed on a mandrel support 3 and direct
wraps of fiber 4 are applied. In the first embodiment of the
invention, a braided carbon fiber material 5 is used, however
either stitched woven fabric forms may be used as long as the
correct fiber architecture can be accommodated. The braided
material lends itself ideally to this application for high pressure
hydrogen storage cylinders as braid fiber architectures have
naturally high permeability for the resin transfer molding's resin
injection cycle, and they can be made with the necessary blend of
fibers for hoop and axial stresses for the cylinder performance.
The braided material is supplied in spools 6 from a common source
braider, which allows the braider to be in production full time and
operate separately from the tank liner 1 wrapping operation.
[0020] This application is unique to the industry, and the process
has several advantages, which include: (A) The braid can be made in
a tubular form with bi-axial and unidirectional fibers located in
the appropriate places for tank stress design optimization as
demonstrated in 5; (B) An additional strip of bi-axial fibers 7 can
be stitched onto the wide format braid 5 to allow build-up of
additional thickness for the tank ends 8, as well as to mitigate
the effect of changing thickness of the fabric where the
uni-directional fibers stop 9 (eliminating a step change in
thickness that exert effects on stress concentrations in the
pressurized tanks); (C) The braided material 5 will effectively
place a double layer of material down at once as the braided
tubular sock 5 will be layed flat onto the liner 1 thereby
improving production rates; (D) The end-contours can be
accommodated by the bi-axial braid deformed with fiber shearing
through an automatic process using fingers 10, which are attached
to cams 13 to draw down and contour to end-domes, and the fiber
ends sealed down by use of a local sealing method, such as adhesive
tacking or other process as common in the industrial practice, and
this method thereby allows precise end-contouring and thickness
control of the material preform; (E) The uni-directional fibers 11
allow the braid to be held under tension during the application.
The tension control is effected through tensioning drag devices 12.
Having controlled and precise tension thereby controls the laminate
net thickness, and this restraint afforded by the uni-directional
fibers 11 prevents the cylinder end wraps 14 from becoming
stretched and wrinkling or moving off-plane from the desired fiber
application location; (F) The bi-axial fibers can be tailored
during the braiding process to optimize the fiber location and
orientation, reducing materials application and cost of the tanks;
(G) The floor area required for the fiber application process is
exceptionally small compared to other filament winding-type
operations, and does not rely on movement of either the braider or
the liner as is the case of a direct braid over-wrap; (H) The
system allows the braid manufacture to be separated from the braid
application process, thereby fully utilizing the braider equipment
in continuous production of materials and also fully utilizing the
liner wrapping equipment in production of over-wrapped liners ready
for molding.
[0021] A unique molding system has been developed that is a
significant departure from any in the state-of-the-art today. The
wrapped dry tank 15 is placed in a cavity mold 16, and is rotated
17 during mold closing 18 to draw tension in the fabric preform.
This allows the part to be enclosed in the tool with no fiber
pinching or deformation occurring and develops and retains tension
required in the fiber, as the fabric ends 27 are drawn down and
into the final cavity shape. The mold segments 25 close
sequentially and the tank rotation 17 is made possible as the boss
ends 2 of the tank liner 1 are exposed to the outside of the mold
16. The mold tooling is constructed of several segments 25, in the
first reduction to practice three segments were used, but
preferentially four segments are used to optimize mold closing
operations.
[0022] The liner of the tank is flooded with heat-transfer fluid 19
through quick-release end connectors 26. The heat transfer fluid 19
has its temperature optimized for resin injection viscosity
control, but still well below the reaction initiation temperature
of the resin components as in the case of thermoset resins. The
heat-transfer fluid 19 is pressurized 22 with pump 20 to allow use
of a thin-wall liner, effectively providing internal support to the
liner during resin injection. Resin injection pressure 23 can then
be optimized and balanced against collapse or dimensional change of
the liner 1 and hence local deformation of the fiber preform,
another common problem with resin transfer molding. The fluid 19
and pressure boost pump 20 also allows for application of internal
vibration assist during injection, another facet unique to the
application in composite storage cylinders. This assist allows for
faster injection, more rapid fiber wet-out, and enhanced release of
voids in the laminate, and is achieved preferentially as a
thin-walled liner is made possible through the invention and the
mold does not need to transfer this vibration through the bulk of
the metal tool 16.
[0023] The next stage of the process occurs upon completion of the
resin injection 23. In the case of thermoset resins, a
high-temperature, pressurized heat transfer fluid 21 is flooded
inside the liner compartment through the same quick release
fittings 26. This hot fluid provides heat to the laminate from
within the liner cavity and thereby initiates the reaction of the
resin components. Excess heat generated during exothermic curing of
the laminate resin will be absorbed back into the heat transfer
fluid 21 through the liner 1, thereby mitigating very high internal
temperatures and the possibility of overheating the laminate during
cure, and also mitigating some of the thermal stresses typical of
cured composites. Similarly, heat loss through system components
can be made up by applying external heat 24, and thus very precise
and also rapidly responding process control is made possible. As
desired, additional pressure 22 can be applied to the
high-temperature heat transfer fluid 21 to ensure hydrostatic
pressures internal to the composite laminate are retained.
[0024] On completion of the cure cycle the cold fluid 19 is
returned to the liner internal cavity. This cools the now fully
cured composite cylinder down to a level whereby the tool opening
and part removal are accomplished as rapidly as possible. Once the
temperature is reduced to an acceptable level, the part is removed
and the tool is ready for the next operation.
[0025] In the case of using a thermoplastic resin, the process is
adapted for a different cycle, but principals common to the plastic
industry are now modified and applied in a unique environment for
achieving rapid processing of fiber-reinforced cylinders. The heat
transfer fluid 21 is pumped through quick release fittings 26 into
the liner 1 internal cavity. This temperature is set to slightly
above the melt temperature of the desired thermoplastic resin.
Resin injection 23 of liquid thermoplastic resin occurs and the
resin permeates the entirety of the laminate as is common in resin
transfer molding, holding the internal pressure 22 and internal
temperature of fluid 21 allows the process to be fully executed and
the laminate completely saturated with resin. On completion of the
injection, cold process fluid 19 is now passed into the liner and
serves to solidify the thermoplastic resin and thus consolidate the
composite laminate without needing to remove a large quantity of
heat through and into the tool 16 walls. As is desired in
thermoplastic molding, high pressure can be held on the laminate
throughout the cooling cycle via pump 20 pressurizing the cavity
22. On acceptable cool-down the part can then be demolded and the
cycle completed.
[0026] This description of the invention has thus been made clear
in illustrative embodiments, and reduced to practice in a composite
high-pressure storage tank: comprising four layers of a braided
triaxial/biaxial fabric as described herein, coupled with resin
transfer molding of a thermoset resin under process control as also
described herein. The individual steps of the process have been
demonstrated to be practical and complete within 30 minutes, an
order of magnitude improvement over the state-of-the-art of
filament winding of high. pressure composite overwrapped gas
storage tanks. Testing of the completed articles was undertaken and
has shown capability to achieve burst pressures of over 4,000 psi
in first article demonstration of the process principles. Thus,
while there will now be immediately obvious to those skilled in the
art many modifications of process, structure, and components as
used in the practice of the invention, these invention
modifications and variations can be made therein without departing
from the spirit and scope of the invention as defined in the
following claims.
* * * * *