U.S. patent application number 10/896234 was filed with the patent office on 2004-12-23 for composite tooling.
Invention is credited to Joseph, Brian E., Rogers, Darren Kenneth.
Application Number | 20040258605 10/896234 |
Document ID | / |
Family ID | 32965655 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040258605 |
Kind Code |
A1 |
Joseph, Brian E. ; et
al. |
December 23, 2004 |
Composite tooling
Abstract
Carbonaceous, composite tooling fabricated from pitch-based or
coal-based cellular or porous products, "carbonaceous foams" having
a density of preferably between about 0.1 g/cm.sup.3 and about 0.8
g/cm.sup.3 that are produced by: 1) conventional pitch foaming
processes or; 2) the controlled heating of coal particulate
preferably up to 1/4 inch in diameter in a "mold" and under a
non-oxidizing atmosphere. According to a specifically preferred
embodiment, the starting material coal has a free swell index as
determined by ASTM test D720 of between about 3.5 and about
5.0.
Inventors: |
Joseph, Brian E.; (Wheeling,
WV) ; Rogers, Darren Kenneth; (Wheeling, WV) |
Correspondence
Address: |
MCGUIREWOODS, LLP
1750 TYSONS BLVD
SUITE 1800
MCLEAN
VA
22102
US
|
Family ID: |
32965655 |
Appl. No.: |
10/896234 |
Filed: |
July 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10896234 |
Jul 22, 2004 |
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09941342 |
Aug 29, 2001 |
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09941342 |
Aug 29, 2001 |
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09902828 |
Jul 10, 2001 |
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6749652 |
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09902828 |
Jul 10, 2001 |
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09453729 |
Dec 2, 1999 |
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Current U.S.
Class: |
423/445R |
Current CPC
Class: |
B22C 9/00 20130101; B32B
5/16 20130101; Y10T 428/8305 20150401; Y10T 428/31815 20150401 |
Class at
Publication: |
423/445.00R |
International
Class: |
C01B 031/00 |
Claims
1-9. (Canceled)
10. Tooling for the fabrication of composite materials comprising a
tool body comprising carbonaceous foam, wherein the carbonaceous
foam provides structural support for at least a portion of the
composite material, and wherein the tool body is adapted for
fabricating members from composite materials.
11. The tooling of claim 10, wherein said carbonaceous foam is
pitch-based or coal-based.
12. The tooling of claim 11, wherein said carbonaceous foam is a
semi-crystalline, largely isotropic, porous coal-based product
produced from particulate coal.
13. The tooling of claim 12, wherein said coal exhibits a free
swell index of about 3.50 to about 5.0.
14. The tooling of claim 11, wherein the carbonaceous foam has a
compressive strength below about 6000 psi.
15. The tooling of claim 11, wherein said carbonaceous foam has
been carbonized.
16. The tooling of claim 11, wherein said carbonaceous foam has
been graphitized.
17. The tooling of claim 10, further comprising a facesheet of a
dissimilar material coated on the tool body.
18. The tooling of claim 10, wherein the density of said
carbonaceous foam varies in density throughout the mass
thereof.
19. The tooling of claim 10, wherein the tool body is formed of
carbonaceous foam that was controllably cooled to a temperature
below about 100.degree. C. at a rate of 10.degree. C./min or more
to provide an outer surface of the carbonaceous foam with a density
higher than a density of an outer surface of the carbonaceous foam
when the carbonaceous foam is cooled at a rate of less than
10.degree. C./min.
20. The tooling of claim 10, wherein the coefficient of thermal
expansion of the carbonaceous foam is substantially similar to the
coefficient of thermal expansion of the composite material.
Description
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 09/453,729 flied Dec. 12, 1999 and U.S. patent
application Ser. No. ______ (not yet assigned) filed Jul. 10, 2001
and entitled "Cellular Coal Products and Processes".
FIELD OF THE INVENTION
[0002] The present invention relates to tooling useful in the
fabrication of structural and other members from composite
materials such as reinforced polymer composites and the like and,
more particularly to such tooling manufactured from carbon
foams.
BACKGROUND OF THE INVENTION
[0003] The fabrication of, for example, structural members from
composite materials generally involves "winding" or otherwise
wrapping or applying a "green" or "prepeg" form of the composite
material upon a mandrel or to other shaped tooling such as a mold,
curing the thus applied composite material and then removing the
shape from the tooling. Many materials and technologies exist for
the production of filament winding mandrels and composite tooling
in instances where production volumes or quantities are large or
where cost is not an issue. More challenging, however, are the
cases of limited production of prototype parts and the refinement
of tooling designs during experimental programs or production
troubleshooting. For example, the military has demonstrated an
interest in developing tooling options for limited quantity
production, depot-level maintenance and the fabrication of tooling
spare parts.
[0004] The properties of such composite tooling include: 1)
tailorable thermal expansion characteristics potentially matching
those of the commonly used carbon-bismaleamide, invar, steel and
aluminum tooling materials commonly in use; 2) compatibility with
high-temperature service to enable adequate curing of a wide
variety of resin systems used in composite fabrication; 3)
machineability to allow on-site repair and modification; and 4)
relatively low cost.
[0005] The molds used in the fabrication and curing of polymer
matrix composites have been constructed from a wide variety of
materials including invar, steel, aluminum, monolithic graphite,
castable ceramics and carbon-epoxy and carbon-bismaleimide systems.
Mold materials must exhibit high flexural and tensile strengths and
durability, but perhaps most importantly, they must possess a
tailorable thermal expansion to match that of the material being
formed. Vacuum integrity and low heat capacity to allow relatively
short heating and cooling times and thereby shorten fabrication
cycles are also of vital importance for such tooling. The tooling
materials of the prior art were often chosen on the basis of one or
two or these desirable properties, such as strength and durability
in the case of metals, at the expense of others such as tailorable
thermal expansion, low heat capacity and ease of modification.
[0006] One attractive such metal mold material is Invar 36, a low
carbon, 36% nickel austenitic steel that exhibits a low coefficient
of thermal expansion (CTE), excellent durability and the ability to
withstand high rates of thermal cycling. Its fundamental
shortcomings are its low thermal conductivity and its weight. It is
five times heavier than carbon-epoxy tooling of the same volume,
therefore often requiring its application over lighter weight
carbon-epoxy backing structures.
[0007] Other approaches to solving the composite tooling issue
include electroforming a thick nickel layer over a mandrel that is
subsequently removed, composite or graphite tooling over which is
sprayed a metallic layer, and plastic faced plaster (PFP. Filament
winding mandrels are often formed from metals, inflatable rubber
bladders, or aluminum honeycombs with fiber-reinforced polymer
facesheets.
[0008] One of the major difficulties with the formation of large
parts is the magnification of any CTE mismatch over a large area.
This results in "spring-back" or "spring-in" as the formed
composite part pulls away from the tool or squeezes the tool,
depending upon the direction of the CTE mismatch. An excessive CTE
on the female mold can cause the part to be crushed or trapped
during cooling, while too low a CTE on the male tool can cause the
part to lock onto the tool. An important consideration that is
often ignored by mold or tooling designers is the anisotropy of
composite CTE. For some polymer matrix composites, the difference
in CTE between reinforcement and matrix directions can be as great
as 72 ppm/.degree. C. An often proposed solution to this issue is
to lower the temperature of the cure process to minimize these
differences, but this is not possible with some resin systems or
practical in terms of the effect on curing time.
[0009] U.S. patent application Ser. No. 09/453,729, filed Dec. 2,
1999 entitled "Cellular Coal Products and Processes" and U.S.
patent application Ser. No. ______ (not yet assigned), filed Jul.
7, 2001 and entitled "Cellular Coal Products and Processes"
describe coal-based cellular or porous products having a density of
preferably between about 0.1 g/cm.sup.3 and about 0.8 g/cm.sup.3
that are produced by the controlled heating of coal particulate
preferably up to 1 mm in diameter in a "mold" and under a
non-oxidizing atmosphere. According to specifically preferred
embodiments, the coal-based starting materials exhibit a "free
swell index" as determined by ASTM test D720 of between about 3.5
and about 5.0. The porous products produced by these processes,
preferably as a net shape or near net shape, can be readily
machined using conventional techniques, adhered and otherwise
fabricated to produce a wide variety of low cost, low density
products, or used in their preformed shape. Such cellular products
have been shown to exhibit compressive strengths of up to about
4000 psi. As described in the foregoing U.S. Patent Applications,
the properties of such coal-based carbon foams, i.e. strength,
thermal conductivity etc. can be tailored within relatively broad
ranges according to the requirements of a particular
application.
[0010] The application of such coal-based carbon foam materials to
tooling for composite materials applications would solve most, if
not all of the problems with the prior art such composite tooling
materials described above.
OBJECT OF THE INVENTION
[0011] It is therefore an object of the present invention to
provide highly improved composite tooling that overcomes a
significant number of the shortcomings of prior art composite
tooling.
SUMMARY OF THE INVENTION
[0012] According to the present invention, there is provided
carbonaceous, composite tooling fabricated from pitch-based or
coal-based cellular or porous products, "carbonaceous foams" having
a density of preferably between about 0.1 g/cm.sup.3 and about 0.8
g/cm.sup.3 that are produced by: 1) conventional pitch foaming
processes or; 2) the controlled heating of coal particulate
preferably up to 1/4 inch in diameter in a "mold" and under a
non-oxidizing atmosphere. According to a specifically preferred
embodiment, the starting material coal has a free swell index as
determined by ASTM test D720 of between about 3.5 and about
5.0.
DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a graph of showing the general relationship
between gas evolution and time/temperature at various operating
pressures and temperatures for the process of the present
invention.
[0014] FIG. 2 is a cross-sectional view of a "mold" containing
powdered coal prior to expansion in accordance with the process of
the present invention.
[0015] FIG. 3 is a cross-sectional view of the "mold" of FIG. 2
subsequent to expansion of the powdered coal in accordance with the
process of the present invention.
[0016] FIG. 4 is a cross-sectional diagram of an extruder suitable
for the production of coal-based porous products in accordance with
the present invention.
[0017] FIG. 5 is a graph of linear expansion versus use temperature
for series of tailored foam tooling in accordance with the present
invention.
DETAILED DESCRIPTION
[0018] The present invention describes tailorable composite
tooling, i.e. tooling suitable for the fabrication of winding
mandrels or other suitable curing tools, fabricated from a
lightweight carbon foam that is produced by the thermal
decomposition and foaming of pitch or coal derivatives under
controlled conditions. The materials described herein are
especially attractive as composite tooling materials because they
offer much lower density than conventional tooling, low, but
tailorable thermal expansion coefficients and thermal
conductivities and good elevated temperature performance. Composite
tooling fabricated from the materials described herein are readily
machined and repaired and produced from very inexpensive raw
materials, i.e. coal or pitch, which are commonly available for
pennies per pound.
[0019] While the foaming process described herein is not readily
portable, the composite tooling materials described herein offer
features that make them amenable to local level fabrication into
composite tooling. For example, the carbon foams can be produced as
large flat sheets, prismatic bricks, or even conformable blanks
that can be readily assembled into larger structures through the
use of, for example, graphite-phenolic adhesives or can be machined
easily into virtually any desired geometry. Conventional machining
practices using carbide tooling and dust removal systems to capture
liberated, health hazard free graphite-like particles can be
applied in the fabrication. Thus, such materials can be fabricated
into large or complex structures from smaller carbon foam building
blocks and additionally adhered to dissimilar facesheet materials,
should this be desirable.
[0020] The composite tooling of the present invention comprises a
tooling structure, be it a mandrel, mold or other suitable forming
structure, fabricated from a pitch-based or coal-based cellular or
porous product, i.e. a foam, having a density of preferably between
about 0.1 g/cm.sup.3 and about 0.8 g/cm.sup.3. According to a
highly preferred embodiment the foam is coal-based and produced by
the controlled heating of coal particulate preferably up to
{fraction (1/4)} inch in diameter in a "mold" and under a
non-oxidizing atmosphere. According to a specifically preferred
embodiment, the starting material is a coal having a free swell
index as determined by the standard ASTM D720 test of between about
3.5 and about 5.0. Such carbon based foams, without further
treatment and/or the addition of strengthening additives exhibit
compressive strengths of up to about 4000 psi. Impregnation with
appropriate materials or the incorporation of various strength
improving additives can further increase the compressive, tensile
and other properties of these cellular materials. Although a wide
variety of coals meeting the foregoing requirements can be use to
produce the carbon foam materials described herein, they are
preferably bituminous, agglomerating coals that have been
comminuted to an appropriate particle size, preferably to a fine
powder below about -60 to -80 mesh.
[0021] The preferred cellular pitch or coal-based materials
described herein are semi-crystalline or more accurately
turbostratically-ordered and largely isotropic i.e., demonstrating
physical properties that are approximately equal in all directions.
The cellular pitch or coal-based products of the present invention
typically exhibit pore sizes on the order of less than 300.mu.,
although pore sizes of up to 500.mu. are possible within the
operating parameters of the processes described. The thermal
conductivities of the cellular pitch or coal-based products are
generally less than about 1.0 W/m/.degree. K. Typically, the
cellular pitch or coal-based products of the present invention
demonstrate compressive strengths on the order of from about 2000
to about 6000 psi at densities of from about 0.4 to about 0.5
g/cm.sup.3.
[0022] It is most desirable to the successful production of
composite tooling of the present invention from the coal-based
foams described herein that the coal starting material exhibit the
previously specified free swell index of between about 3.5 and
about 5.0 and preferably between about 3.75 and about 4.5.
Selection of starting materials within these parameters was
determined by evaluating a large number of coals characterized as
ranging from high to low volatiles. In general, it has been found
that bituminous coals exhibiting free swell indexes within the
previously specified ranges provided the best foam products for the
production of composite tooling in that they exhibit the lowest
calcined foam densities and the highest calcined foam specific
strengths (compressive strength/density). Coals having free swell
indices below these preferred ranges may not agglomerate properly
leaving a powder mass or sinter, but not swell or foam, while coals
exhibiting free swell indices above these preferred ranges may
heave upon foaming and collapsed upon themselves leaving a dens
compact. Pitch-based foams that can be successfully used in
accordance with the present invention must exhibit the properties
described hereinabove and hereinafter for the carbonaceous foams
suitable for the fabrication of composite tooling and are in turn
prepared using conventional pitch foaming techniques well known in
the carbon arts.
[0023] The preferred coal-based foam production method of the
present invention comprises: 1) heating a coal particulate of
preferably small i.e., less than about 1/4 inch particle size in a
"mold" and under a non-oxidizing atmosphere at a heat up rate of
from about 1 to about 20.degree. C. to a temperature of between
about 300 and about 700.degree. C.; 2) soaking at a temperature of
between about 300 and 700.degree. C. for from about 10 minutes up
to about 12 hours to form a preform or finished product; and 3)
controllably cooling the preform or finished product to a
temperature below about 100.degree. C. The non-oxidizing atmosphere
may be provided by the introduction of inert or non-oxidizing gas
into the "mold" at a pressure of from about 0 psi, i.e., free
flowing gas, up to about 500 psi. The inert gas used may be any of
the commonly used inert or non-oxidizing gases such as nitrogen,
helium, argon, CO.sub.2, etc.
[0024] It is generally not desirable that the reaction chamber be
vented or leak during the heating and soaking operation. The
pressure of the chamber and the increasing volatile content therein
tends to retard further volatilization while the cellular product
sinters at the indicated elevated temperatures. If the furnace is
vented or leaks during soaking, an insufficient amount of volatile
matter may be present to permit inter-particle sintering of the
coal particles thus resulting in the formation of a sintered powder
as opposed to the desired cellular product. Thus, according to a
preferred embodiment of the present process, venting or leakage of
non-oxidizing gas and generated volatiles is inhibited consistent
with the production of an acceptable cellular product.
[0025] Additional more convention blowing agents may be added to
the particulate prior to expansion to enhance or otherwise modify
the pore-forming operation.
[0026] The term "mold", as used herein is meant to define a
mechanism for providing controlled dimensional forming of the
expanding coal. Thus, any chamber into which the coal particulate
is deposited prior to or during heating and which, upon the coal
powder attaining the appropriate expansion temperature, contains
and shapes the expanding porous coal to some predetermined
configuration such as: a flat sheet; a curved sheet; a shaped
object; a building block; a rod; tube or any other desired solid
shape can be considered a "mold" for purposes of the instant
invention.
[0027] As will be apparent to the skilled artisan familiar with
pressurized gas release reactions, as the pressure in the reaction
vessel, in this case the mold increases, from 0 psi to 500 psi, as
imposed by the non-oxidizing gas, the reaction time will increase
and the density of the produced porous coal will increase as the
size of the "bubbles" or pores produced in the expanded coal
decreases. Similarly, a low soak temperature at, for example about
400.degree. C. will result in a larger pore or bubble size and
consequently a less dense expanded coal than would be achieved with
a soak temperature of about 600.degree. C. Further, the heat-up
rate will also affect pore size, a faster heat-up rate resulting In
a smaller pore size and consequently a denser expanded coal product
than a slow heat-up rate. These phenomenon are, of course, due to
the kinetics of the volatile release reactions which are affected,
as just described, by the ambient pressure and temperature and the
rate at which that temperature is achieved. These process variables
can be used to custom produce the expanded coals of the present
invention in a wide variety of controlled densities, strengths etc.
These results are graphically represented in the Figure where the X
axis is gas release, the Y axis is time and the individual curves
represent different pressures of inert gas P.sub.1, P.sub.2, and
P.sub.3, different heat-up rates HR.sub.1, HR.sub.2, and HR.sub.3,
and P.sub.1<P.sub.2<P.sub.3 and
HR.sub.1<HR.sub.2<HR.sub.3.
[0028] Cooling of the composite tooling preform or composite
tooling product after soaking is not particularly critical except
as it may result in cracking of the composite tooling preform or
product as the result of the development of undesirable thermal
stresses. Cooling rates less than 10.degree. C./min to a
temperature of about 100.degree. C. are typically used to prevent
cracking due to thermal shock. Somewhat higher, but carefully
controlled, cooling rates may however, be used to obtain a "sealed
skin" on the open cell structure of the product as described below.
The rate of cooling below 100.degree. C. is in no way critical.
[0029] After expanding the coal particulate as just described, the
porous coal product is an open celled material. Several techniques
have been developed for "sealing" the surface of the open celled
structure to improve its adhesive capabilities, for example, for
the application of facesheets of dissimilar materials for further
fabrication and assembly of a number of parts. For example, a layer
of a commercially available graphitic adhesive can be coated onto
the surface and cured at elevated temperature or allowed to cure at
room temperature to provide an adherent skin. Alternatively, the
expansion operation can be modified by cooling the expanded coal
product or preform rapidly, e.g., at a rate of 10.degree. C./min or
faster after expansion. It has been discovered that this process
modification results in the formation of a more dense skin on the
preform or product which presents a closed pore surface to the
outside of the preform or product. At these cooling rates, care
must be exercised to avoid cracking of the preform or product.
[0030] After expanding, the porous coal-based preform or product is
readily machineable, sawable and otherwise readily fabricated using
conventional fabrication techniques to fabricate the composite
tooling described herein.
[0031] Subsequent to production of the preform or product as just
described, the preform or product may be subjected to carbonization
and/or graphitization according to conventional processes to obtain
particular properties desirable for specific composite tooling
applications. Additionally, a variety of additives and structural
reinforcers may be added to the coal-based preforms or products
either before or after expansion to enhance specific mechanical
properties such as fracture strain, fracture toughness and impact
resistance should these be required for a particular composite
tooling application. For example, particles, whiskers, fibers,
plates, etc. of appropriate carbonaceous or ceramic composition can
be incorporated into the porous coal-based composite tooling
preform or product to enhance its mechanical properties.
[0032] The open celled, coal-based composite tooling preforms or
products of the present invention can additionally be Impregnated
with, for example, petroleum pitch, epoxy resins or other polymers
using a vacuum assisted resin transfer type of process. The
incorporation of such additives provides load transfer advantages
similar to those demonstrated in carbon composite materials. In
effect a 3-D composite is produced that demonstrates enhanced
impact resistance and load transfer properties should these be
required by a particular tooling application.
[0033] The cooling step in the expansion process results in some
relatively minimal shrinkage on the order of less than about 5% and
generally in the range of from about 2% to about 3%. This shrinkage
must be accounted for in the production of near net shape composite
tooling preforms or final products of specific dimensions and is
readily determinable through trial and error with the particular
coal starting material being used. The shrinkage may be further
minimized by the addition of some inert solid material such as coke
particles, ceramic particles, ground waste from the coal expansion
process etc. as is common practice in ceramic fabrication so long
as such additions do not adversely affect the thermal conductivity
or elevated temperature performance of the tooling.
[0034] Carbonization, sometimes referred to as calcining, is
conventionally performed by heating the preform or product under an
appropriate inert gas at a heat-up rate of less than about
5.degree. C. per minute to a temperature of between about
800.degree. C. and about 1200.degree. C. and soaking for from about
1 hour to about three or more hours. Appropriate inert gases are
those described above that are tolerant of these high temperatures.
The inert atmosphere is supplied at a pressure of from about 0 psi
up to a few atmospheres. The carbonization/calcination process
serves to remove all of the non-carbon elements present in the
preform or product such as sulfur, oxygen, hydrogen, etc that might
adversely affect the tooling in its application.
[0035] Graphitization, commonly involves heating the preform or
product either before or after carbonization at heat-up rate of
less than about 10.degree. C. per minute, preferably from about
1.degree. C. to about 5.degree. C. per minute, to a temperature of
between about 1700.degree. C. and about 3000.degree. C. in an
atmosphere of helium or argon and soaking for a period of less than
about one hour. Again, the inert gas may be supplied at a pressure
ranging from about 0 psi up to a few atmospheres.
[0036] The preferred, coal-based porous composite tooling preforms
and products of the present invention can be produced in any solid
geometric shape. Such production is possible using any number of
modified conventional processing techniques such as extrusion,
injection molding, etc. In each of such instances, the process
must, of course, be modified to accommodate the processing
characteristics of the starting material coal. For example, in
extruding such products, as described below, the coal powder
starting material is fed by an auger into an expansion chamber
where it is expanded and from which it is extruded while still
viscous. Upon exiting the extrusion die, the material is cooled to
provide a solid shape of the desired and precalculated dimensions.
To improve the efficiency, i.e., cycle time of the process, the
input material can be preheated to a temperature below the
expansion point, e.g., below about 300.degree. C., fed into the
auger chamber where additional heat is imparted to the powder with
final heating being achieved just before extrusion through the
die.
[0037] Similar relatively minor process modifications can be
envisioned to fabricate the carbon foams of the present invention
for use as composite tooling in injection molding, casting and
other similar conventional material fabrication processes.
[0038] As mentioned above, the carbonaceous foam materials of the
present invention may be coated with a wide variety of facesheet
materials. Such facesheet coatings include, for example, but not
exclusively, Kevlar.RTM. reinforced carbonaceous foam, laminated
E-glass reinforced vinyl esters, Thermal spray applied coatings of
a metal, for example, aluminum or inconel etc. to achieve surface,
heat transfer or thermal expansion properties compatible with
specific composite materials formed on composite tooling produced
as described herein. Such layers can be adhered to the carbonaceous
foam core using any of a wide variety of, for example,
graphite-epoxy adhesives available commercially.
[0039] As a further enhancement of the properties of the composite
tooling described herein, functionally graded foams of varying
density at their surfaces or throughout their structure may be
prepared as described in copending U.S. patent application Ser. No.
09/733,602, filed Dec. 8, 2000. According to this invention,
coal-based cellular products having integral stiffeners or load
paths, directed heat transfer paths and directed mass transfer
paths are provided through the placement of coal-based cells of a
different size and/or density than those making up the matrix of
the product during manufacture. There is also provided a method for
the production of coal-based cellular products possessing these
characteristics. The method described in this application utilizes
the ability to select and design such properties through the proper
selection and control of cell size and density. Such control of
cell size and density is in turn achieved through appropriate
selection of starting materials, starting material particle size,
mold packing and processing parameters. This application is
incorporated herein in its entirety.
[0040] The following examples will serve to illustrate the practice
of the invention.
EXAMPLES
Example 1
[0041] As shown in FIG. 2, a layer 10 of comminuted bituminous coal
having a free swell index of about 4 and ground to a particle size
of about 60 mesh and about 2 inch deep is deposited in mold 12
equipped with a cover 16. Mold 12 is assembled from three
individual pieces carbon or tool steel pieces, sides 12A and 12B
and bottom 12C, all joined together by bolts 11 and lined with a
ceramic glaze or spray applied ceramic lining 13. Cover 16 includes
a similar interior ceramic lining 15 and is attached to sides 12A
and 12B with bolts 17 in the final assembly prior to heating.
Gaskets 19 are preferably used to insure a tight fit of cover 16
onto sides 12A and 12B. Cover 16 is optionally equipped with a
sintered vent plug 20 to permit purging of the interior of mold 12
with non-oxidizing gas. This configuration, incorporating valve 20
also permits pressurization, if desired to control expansion speed
and/or pore size in the final product as described hereinabove.
Nitrogen gas is repeatedly introduced through valve 20 to assure
that all oxygen in mold 12 is purged (generally 2-4 such purges
have been found satisfactory) and to provide a one atmosphere
pressure of nitrogen inside of mold 12. Mold 12 is then heated at a
rate of from about 1 to about 10.degree. C./min up to a temperature
of about between about 450 and 600.degree. C. and held at this
temperature sufficient to devolatalize and sinter the cellular
product (generally less than about one hour). This treatment
results in the production of an open celled expanded coal product
10A as shown in FIG. 3. Mold 12 is then cooled to room temperature
at a rate of less than about 10.degree. C./min. to a temperature of
100.degree. C.; any remaining pressure is then vented through valve
15 and the sample removed from mold 12 by disassembly of mold 12 by
disengagement of bolts 11. Expanded coal product 10A is thereby
readily removed from mold 14 and is subsequently sawed to the
desired dimensions.
[0042] Product 10A has a density of between about 0.4 and about 0.6
g/Cm.sup.3 and demonstrates a compressive strength on the order of
between about 2000 and 6000 psi. Thermal conductivity as determined
by the guarded heat flow method is below about 1.0 W/m/K.
Example 2
[0043] The application of the process of the present invention in
an extrusion process is depicted in FIG. 4. As shown in that
figure, comminuted bituminous coal 22 of a particle size of about
-80 mesh is introduced via hopper 24 into chamber 26 equipped with
auger 28 that moves particulate coal 18 through chamber 26 and into
expansion chamber 30. Chamber 26 is heated by means of a series of
barrel heaters 32, 34 and 36 to impart a temperature of less than
about 300.degree. C. to particulate coal 18 as it approaches and
enters expansion chamber 26. As is conventional practice in
extrusion, chamber 26 is divided into a feed section, a compression
section and a metering section each defined roughly by the location
of barrel heaters 32, 34 and 36 and imparted by the tapered shape
of auger 28. Expansion chamber 30 is maintained under a
non-oxidizing atmosphere and at a temperature of about 450.degree.
C. by means of barrel heater 38. Particulate coal 18 expands within
chamber 26 to form expanded coal product 40 and, while still
viscous, expanded coal product 40 is extruded through a die 42 to
form solid shaped product 44 upon cooling to room temperature.
Solid shaped product 44 demonstrates properties similar to those
obtained from the product described in Example 1.
[0044] At the point where particulate coal 22 exits chamber 26 and
enters expansion chamber 30, chamber 26 is preferably equipped with
a breaker plate 46 that serves to break up any large agglomerates
of particulate coal 22 that may have formed in transit within
chamber 26.
[0045] Cellular coal-based extrudate 44 may have virtually any
solid shape ranging from a large flat panel 4'.times.8' as might be
used as the core of the above-described building panel to square
shapes, rounds, channels and even tubular shapes if a bridge die is
used in the extrusion process. Almost any shape that can be
achieved with plastic or metal extrusion can be similarly obtained
using the process of the present invention.
[0046] A variety of carbonaceous foams exhibiting varying percent
linear expansions can be produced and used in accordance with the
successful practice of the present invention, i.e. the linear
expansion can be tailored to meet the needs of any particular
composite being fabricated on tooling produced in accordance with
the present invention. A spectrum of such materials are shown in
FIG. 5 which is a graph of linear expansion versus temperature for
sample tooling produced from carbonaceous foams in accordance with
the present invention.
[0047] As the invention has been described, it will be apparent to
those skilled in the art that the same may be varied in many ways
without departing from the spirit and scope of the invention. Any
and all such modifications are intended to be included within the
scope of the appended claims.
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