U.S. patent application number 11/054818 was filed with the patent office on 2006-08-10 for method of manufacturing composite panels.
This patent application is currently assigned to Merkel Composite Technologies, Inc.. Invention is credited to Michael Merkel.
Application Number | 20060175730 11/054818 |
Document ID | / |
Family ID | 36779140 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060175730 |
Kind Code |
A1 |
Merkel; Michael |
August 10, 2006 |
Method of manufacturing composite panels
Abstract
A method of manufacturing solid composite panels utilizes an
exothermic foam-forming resin to simultaneously consolidate and
cure the heat activated resin of the composite panel without
forming a foam-filled part. According to the method, composite
fabric layers are laid up on the interior surface of a mold half
that conforms to the surface configuration of the finished panel.
Once the composite fabric layers are laid up, a flexible bladder is
placed over the composite layup and the mold closed. The exothermic
foam-forming resin is injected into the bladder within the mold
cavity, which generates heat to cure the resin impregnated fabric
layers above the cure temperature while simultaneously generating
pressure within the cavity to consolidate the fabric layers into a
substantially solid void-free composite panel.
Inventors: |
Merkel; Michael; (Phoenix,
AZ) |
Correspondence
Address: |
John D. Titus;THE CAVANAGH LAW FIRM.
Ste. 2400
1850 N. Central Avenue
Phoenix
AZ
85004
US
|
Assignee: |
Merkel Composite Technologies,
Inc.
Phoenix
AZ
|
Family ID: |
36779140 |
Appl. No.: |
11/054818 |
Filed: |
February 10, 2005 |
Current U.S.
Class: |
264/257 ;
264/324 |
Current CPC
Class: |
B29C 70/44 20130101;
B29C 33/505 20130101; B29C 33/38 20130101; B29C 33/3821 20130101;
B29C 44/16 20130101 |
Class at
Publication: |
264/257 ;
264/324 |
International
Class: |
D21J 3/00 20060101
D21J003/00 |
Claims
1. A method of manufacturing a composite panel having a first side
and a second side comprising: providing a first mold half having an
interior surface defining the surface configuration of said first
side of said composite panel; applying at least one fabric layer to
said interior surface of said first mold half, said at least one
fabric layer comprising a plurality of fibers coated with a heat
curable resin; providing a second mold half; joining said first
mold half and second mold half together to provide a substantially
sealed interior volume; inserting a bladder into said interior
volume in contact with said at least one fabric layer; injecting a
catalyzed self-expanding exothermic foam material into said bladder
in an amount sufficient to pressurize said interior volume to a
predetermined pressure and to simultaneously heat said heat curable
resin to a predetermined temperature; allowing said heat curable
resin to cure to form said composite panel; and separating said
foam material from said cured composite panel.
2. The method of claim 1 further comprising: applying a non-stick
layer between said bladder and said at least one fabric layer.
3. The method of claim 2, wherein: said non-stick layer comprises a
woven glass fabric impregnated with a tetrafluoroethylene
polymer.
4. The method of claim 2 further comprising: allowing said
catalyzed self-expanding exothermic foam material to cure into a
rigid volumetric body and thereafter detaching said rigid
volumetric body from said at least one fabric layer.
5. The method of claim 1 further comprising: applying a
substantially non-expanding exothermic gel coat layer between said
at least one fabric layer and said interior surface of said first
mold half.
6. The method of claim 1 further comprising: Applying a
substantially non-expanding exothermic resin between said at least
one fabric layer and said bladder.
7. The method of claim 1, wherein: said heat curable resin is
applied to said plurality of fibers of said at least one fabric
layer before said at least one fabric layer is applied to said
interior surface of said first mold half.
8. The method of claim 1, wherein: said heat curable resin is
applied to said plurality of fibers of said at least one fabric
layer after said at least one fabric layer is applied to said
interior surface of said first mold half.
9. The method of claim 1, wherein: said interior surface defining
the surface configuration of said first side of said composite
panel comprises a surface defining a residential door skin.
10. The method of claim 1, wherein: said interior surface defining
the surface configuration of said first side of said composite
panel comprises a surface defining a leg brace.
11. The method of claim 1, wherein: said catalyzed self-expanding
exothermic foam material has an exothermic rate sufficient to
maintain said heat curable resin at a temperature of least 150
degrees Fahrenheit for a minimum of 30 minutes.
12. The method of claim 1, wherein: said composite panel comprises
an orthopedic brace.
13. The method of claim 1, wherein: said composite panel comprises
a residential door skin.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to the fabrication of
composite panels, more particularly to the manufacture of composite
panels for use in medical equipment and residential
construction.
[0002] In U.S. Pat. No. 6,117,376 (the "376 patent") the inventor
of the present invention describes a method of making foam-filled
composite products, in which fiber layers, impregnated with a heat
activated resin are built up on two mold halves, which are then
clamped together to form a pressure vessel. An exothermic
foam-forming resin is then poured into the mold cavity. The
exothermic foaming reaction of the foam material generates both
heat and pressure to consolidate and cure the resin impregnated
fiber layers while forming a tight bond between the foam and the
fiber layers. Advantages of the method described in the '376 patent
includes substantial savings in production costs by obviating the
need for expensive autoclaves, vacuum furnaces, heated molds or
other capital-intensive equipment.
[0003] There are, however, applications where a solid composite
panel, rather than a foam-filled composite structure, may be
advantageously used. Unfortunately, to manufacture thin composite
panels prior to the present invention, one had to resort to the
capital equipment-intensive methods such as vacuum furnaces and
autoclaves. What is needed, therefore, is a method of making solid
composite panels utilizing a self-heating and pressurizing method
similar to that taught in the '376 patent.
SUMMARY OF THE INVENTION
[0004] The present invention comprises a method of manufacturing
solid composite panels utilizing an exothermic foam-forming resin
to simultaneously consolidate and cure the heat activated resin of
the composite panel without forming a foam-filled part. According
to an illustrative embodiment of the present invention, composite
fabric layers are laid up on the interior surface of a mold half
that conforms to the surface configuration of the finished panel.
The composite fabric layers may be so-called "pre-preg" sheets,
which comprise fabric that has been pre-coated with resin, or they
may be dry sheets that are wetted with resin after they have been
placed in the mold half. Once the composite fabric layers are laid
up, a flexible bladder is placed over the composite layup and the
mold closed by means of a rigid cover plate so as to form a cavity
inside the mold. A foam-forming resin, is pre-measured so as to
expand to more than fill the cavity. The foam-forming resin is
injected into the bladder within the mold cavity. The mix begins
foaming after a short delay, generating an exothermic reaction that
heats the resin impregnated fabric layers above the cure
temperature. Simultaneously, the expanding foam generates pressure
within the cavity. The heat generated by the exothermic reaction
initiates and maintains curing of the wet resin because the thermal
energy is largely retained within the mold. The internal
pressurization simultaneously consolidates the fabric layers into a
substantially solid void-free composite panel. A post-curing
interval can be employed to assure full stabilization of the
composite product. Thereafter, the mold may be opened and the
product released from the mold, and the foam-filled bladder
discarded.
[0005] Because the mold half and the cover plate have strong
pressure resistant outer walls, but only the interior portion of
the mold half needs to have a precise, part-forming shape, the
outer wall of the mold half and the cover plate can be reused for a
variety of similar applications. Virtually no capital equipment is
required for the manufacture of the molds or parts in small or
large quantities. No external power is required to generate heat or
pressure. In consequence, a wide variety of composite parts
heretofore requiring massive capital investment for autoclaves,
vacuum furnaces and the like can be manufactured on site with
minimal equipment and investment.
BRIEF DESCRIPTION OF THE DRAWING
[0006] The present invention will be better understood from a
reading of the following detailed description, taken in conjunction
with the accompanying drawings figures in which like references
designate like elements and, in which:
[0007] FIG. 1 is an exploded perspective view of a mold for
manufacturing a composite panel incorporating features of the
present invention;
[0008] FIG. 2 is a partial cross-sectional view of the mold of FIG.
1 in a closed condition;
[0009] FIG. 3 is a perspective view of a composite panel
manufactured in accordance with the teachings of the present
invention;
[0010] FIG. 4 is an enlarged cross-sectional view of a composite
panel manufactured in accordance with the teachings of the present
invention;
[0011] FIG. 5 is a partial cross-sectional view of an alternative
embodiment of a mold for manufacturing composite products
incorporating features of the present invention; and
[0012] FIG. 6 is an exploded perspective view of an alternative
embodiment of a mold for manufacturing composite panels
incorporating features of the present invention.
DETAILED DESCRIPTION
[0013] The drawing figures are intended to illustrate the general
manner of construction and are not necessarily to scale. In the
detailed description and in the drawing figures, specific
illustrative examples are shown and herein described in detail. It
should be understood, however, that the drawing figures and the
detailed description are not intended to limit the invention to the
particular form disclosed, but are merely illustrative and intended
to teach one of ordinary skill how to make and/or use the invention
claimed herein and for setting forth the best mode for carrying out
the invention.
[0014] With reference to FIGS. 1-3, medical devices such as
orthopedic leg braces must be strong and durable in order to
provide the necessary protection for the wearer. At the same time,
such devices must be made of lightweight materials to provide
maximum comfort. Accordingly, lightweight, high-strength composites
such as graphite-epoxy are increasingly being used in the main
structural components of these devices. Generally, orthopedic
devices are custom-fitted to the patient. Since the doctor's office
does not have the manufacturing facilities on-site, typically the
doctor or the doctor's assistant must take the appropriate
measurements, which are transmitted offsite to the fabricator. The
fabricator then molds the parts or selects pre-fabricated
components based on the measurements and assembles them into a
device having the appropriate dimensions. Because the doctor's
office and the fabricator are often hundreds or thousands of miles
away, turnaround time is slow and, since prior art fabrication
techniques are used to mold the components, the resulting product
is unnecessarily bulky and/or costly.
[0015] In accordance with the present invention, a composite panel
such as leg brace 10 can be fabricated on-site at the doctor's
office with a minimum investment in capital-equipment by a
technician with minimal training. A mold assembly 13 consisting of
a lower mold half 12 and an upper mold half such as mold cover 14
comprise the only capital equipment necessary to carry out the
molding process. Preferably lower mold half 12 and mold cover 14
are themselves made of carbon fiber composite, ceramic,
ceramic-lined metal or other durable material having a low thermal
conductivity. Inner surface 16 of lower mold half 12 comprises a
female mold portion 18 that conforms to the configuration of outer
surface 20 of leg brace 10. Preferably female mold portion 18
comprises a silicone line 22 placed within lower mold half 12.
Silicone liner 22 has an outer surface that matches the recess in
lower mold half 12 and an inner surface that is cast to conform to
the custom dimension of the leg brace being fabricated. Use of
replaceable silicone liners within mold half 12 permits lower mold
half 12 to be utilized for fabricating a wide variety of shapes and
sizes, thus permitting leg brace 10 to be customized to each
individual patient.
[0016] A first fabric layer 24 is placed inside lower mold half 12
within the recess defined by female mold portion 18 of silicone
liner 22. First fabric layer 24 may be made from any of a wide
variety of structural fabric materials such as carbon fiber, aramid
fiber, glass fiber and ceramic fiber is either dry or "pre-preg"
(pre-impregnated with resin) sheets. In the illustrative
embodiment, first fabric layer 24 comprises a pre-preg sheet of
woven bi-directional 0.006 inch bi-directional carbon fiber, coated
with a B-Staged (i.e., heat activated) epoxy resin sold by Cass
Polymers, of Charlotte Mich. under the trade mark PROBUILD, however
other fibrous materials and resin systems such as 0.006 inch
uni-directional carbon fiber, glass fiber, aramid fiber, ceramic
fiber or other flexible fabric materials coated with heat-activated
resins may be used without departing from the scope of the present
invention.
[0017] One or more immediate fabric layers such as fabric layer 26
are positioned atop first fabric layer 24 within lower mold half
12. Fabric layer 26 also may comprise any of a wide variety of
structural fabric materials such as graphite fiber, aramid fiber,
glass fiber, or ceramic fiber, but in the illustrative embodiment
comprises a pre-preg sheet of uni-directional graphite material
such as C.F. 7440-44-0 made by Hexcel Composites of Stamford Conn.,
coated with a B-Staged epoxy such as the aforementioned PROBUILD
epoxy resin. Depending on the application, additional layers of
uni- and bi-directional structural fabric may be added to achieve
the strength and rigidity needed for the particular application.
Once the proper number of layers have been built up within lower
mold half 12, a mold release layer 28 is positioned over the
structural fabric layers 24 and 26. Depending on the desired
finish, mold release layer 28 may be any number of film or woven
sheets designed for such purposes such as mylar, which yields a
glossy surface or polytetrafluoroethylene mold release sheets
manufactured by Precision Coatings, Inc. of Walled Lake, Mich. Mold
release layer 28 freely releases from the resins that are cured in
direct contact with its surface while having the additional
advantage of avoiding contamination of the resin surface with
release agents such as wax based materials.
[0018] A bladder 30 is then place atop mold release layer 28. In
the illustrative embodiment, bladder 30 comprises a polyethylene
bag having a volume substantially in excess of the cavity defined
by inner surface 16 of lower mold half 12. Bladder 30 is then
filled with a pre-measured portion of an exothermic foam-forming
resin 34 such 20-10 foam resin manufactured by Polytech Foam
Products, Inc. a division of FAI International, of Richmond Calif.
Typical foam resins expand to form a foam having a density from 2
pounds per cubic foot to 24 pounds per cubic foot and can be
selected based on the desired pressure and heat to be exerted on
the fabric layers. Before the foam material expands significantly,
mold cover 14 is attached to mold lower half 12 by means of screws,
clamps or otherwise such that inner surface 16 of lower mold half
12 forms a substantially sealed interior volume 32.
[0019] The foam-forming resin 34 begins to expand rapidly and
builds up interior pressure within interior volume 32 thus
consolidating fabric layers 24-26 into a solid void-free body. The
reaction of the foam-forming resin 34 is also strongly exothermic
and heats the foam to an excess of 300.degree. F. as it expands.
The heat from the foam-forming resin 34 is conducted easily through
bladder 30 into the resin surrounding the fabric layers 24-26. The
insulating properties of lower mold half 12 and mold cover 14
retain the heat within the interior volume 32 such that the
temperature in the resin surrounding fabric layers 24-26 remains
above the heat activation/curing temperature for a pre-determined
period of time long enough to ensure full curing of the resin.
[0020] Once the resin surrounding fabric layers 24-26 is fully
cured, mold cover 14 is removed and the cured part consisting of
fabric layers 24-26 is removed from lower mold half 12. Bladder 30
containing the now-cured foam-forming resin 34 is then separated
from cured leg brace 10 and is discarded, as is mold release layer
28. The final part is then used as-cast or is finished with paint,
gel coat or other surface finish.
[0021] With reference to FIG. 4, in order to increase the part
thickness without adding additional often costly layers of carbon
fabric, an intermediate layer 36 may be added between various
layers of fabric layer 26. In one embodiment, intermediate layer 36
comprises an exothermic non-foaming fast-setting urethane polymer,
which acts as a spacer between fabric layers 26 to increase the
cross sectional moment of inertia thereof. The exothermic nature of
the urethane intermediate layer 36 also assists in elevating the
temperature of the resin surround fabric layers 24-26 to above
their cure temperatures. It is not necessary, however, that
intermediately layer 36 be an exothermic urethane resin. Other
filler materials including fiberglass cloth or other cloth
materials less costly than carbon fiber may be used as intermediate
layer 36.
[0022] Since exothermic foam-forming resin 34 assumes whatever
irregular shape is present within interior volume 32 of lower mold
half 12, it is possible to use the exothermic foam reaction to
consolidate and heat multiple parts at once. With reference to FIG.
5, a pair of leg braces 40-42 may be cured simultaneously by laying
up leg brace 40 in lower mold half 12 than laying up a second leg
brace 42 in a mold cover 38 that is identically contoured to lower
mold half 12. Once the mold is closed and the exothermic
foam-forming resin 34 is injected into bladder 30 contained within
lower mold half 12 and mold cover 38 the exothermic foam-forming
resin 34 simultaneously heats the resin surrounding the fabric
layers comprising leg brace 40 and 42 while simultaneously heating
the resin to above the cure temperature until the resin is fully
cured. Once the mold is opened and bladder 10 containing the cured
foam-forming resin 34 is separated and discarded, leg brace 40 is
separated from lower mold half 12 and a second leg brace 42 is
removed from mold cover 38.
[0023] With reference to FIG. 6, implicit in the discussion of
FIGS. 1-5, an advantage of using an exothermic foam-forming resin
to pressurize the interior volume 32 of the mold is that the
pressure generated by the foam is omni-directional and, therefore,
consolidates the fabric layers irrespective of their orientation. A
process in accordance with the present invention can, however,
equally apply to a relatively flat panel such as a door skin 50 as
shown in FIG. 6. As with the illustrative embodiment of FIGS. 1-5,
the process begins with providing a lower mold half 54, the
interior surface of which defines the final surface configuration
of door skin 50. Because the surface finish of door skin 50 is
critical, however, a gel coat such as ES 201 PC Surface Coat
manufactured by Cass Polymers, of Charlotte Mich. is applied to the
interior surface 56 of lower mold half 54. Since the gel coat 62
undergoes a catalyzed exothermic reaction, the gel coat 62 also
assists in the heating of the interior volume 58 of mold assembly
60. Once gel coat 62 has been applied to interior surface 56 of
lower mold half 54, a first fabric layer 52 preferably a plurality
of fabric layers are laid-up in lower mold half 54. Thereafter
bladder 64 containing a pre-measured quantity of exothermic
foam-forming resin 66 is placed inside interior volume 58 of lower
mold half 54. Thereafter, mold cover 68 is placed over lower mold
half 54 and clamped or bolted together. As with the illustrative
embodiment of FIGS. 1-5, a mold release layer optionally may be
used to prevent bladder 64 for adhering to door skin 50 during the
curing operation. Also, as with the illustrative embodiment of
FIGS. 1-5, within the sealed interior volume 58 of mold assembly
60, the exothermic foam-forming resin 66 expands and pressurizes
interior volume 58 of mold assembly 60 consolidating the fabric
layers of door skin 50 and simultaneously heating the resin to
above the cure temperature. Once the resin in the fabric layers of
door skin 50 is fully cured, mold assembly 60 is opened and bladder
64 containing the now-cured exothermic foam-forming resin 66 is
removed together with the completed door skin 50. Bladder 64
together with the cured exothermic foam-forming resin 66 is then
separated from door skin 50 and discarded leaving the door skin 50
complete and ready to use.
[0024] Although certain illustrative embodiments and methods have
been disclosed herein, it will be apparent from the foregoing
disclosure to those skilled in the art that variations and
modifications of such embodiments and methods may be made without
departing from the spirit and scope of the invention. Accordingly,
it is intended that the invention should be limited only to extent
required by the appended claims and the rules and principals of
applicable law.
* * * * *