U.S. patent application number 09/760967 was filed with the patent office on 2001-07-05 for method and apparatus for producing gas occlusion-free and void-free compounds and composites.
Invention is credited to Bendek, Wilfredo G., Dufeu, Jorge L., Vidaurre, Victor H..
Application Number | 20010006991 09/760967 |
Document ID | / |
Family ID | 21862623 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006991 |
Kind Code |
A1 |
Vidaurre, Victor H. ; et
al. |
July 5, 2001 |
Method and apparatus for producing gas occlusion-free and void-free
compounds and composites
Abstract
The present invention discloses a generic method for producing
void and gas occlusion free materials, as well as apparatuses for
batch and continuous production of same. This generic method can be
utilized in the production of a wide variety of polymeric compounds
and composites and specifically encompasses the two ends of the
polymeric composite spectrum, that is, polymer concretes on the one
hand, and fiber-reinforced polymer composites on the other. The
composite materials of the present invention are characterized by
visual count as being void and gas occlusion free to the level of 1
micron at 1250.times. magnification. Concomitantly, the invention
produces useful polymer concrete materials which exhibit
substantially improved integrity for easy machining at high speeds,
and high dielectric and mechanical strength, as compared with
composite materials produced by conventional methods. Thus, one
particularly well-suited application for the materials of the
present invention is the class of high voltage electrical
insulating materials and insulators where the presence of voids, or
gas occlusion flaws, may have deleterious effects, leading to their
early failure.
Inventors: |
Vidaurre, Victor H.;
(Santiago, CL) ; Bendek, Wilfredo G.; (Santiago,
CL) ; Dufeu, Jorge L.; (Santiago, CL) |
Correspondence
Address: |
RADER, FISHMAN & GRAUER PLLC
39533 WOODWARD AVENUE
SUITE 140
BLOOMFIELD HILLS
MI
48304-0610
US
|
Family ID: |
21862623 |
Appl. No.: |
09/760967 |
Filed: |
January 16, 2001 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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09760967 |
Jan 16, 2001 |
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09032009 |
Feb 27, 1998 |
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6218458 |
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09032009 |
Feb 27, 1998 |
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08863902 |
May 27, 1997 |
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6046267 |
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Current U.S.
Class: |
524/494 ;
264/102; 264/240; 264/255; 264/257; 34/443; 65/476 |
Current CPC
Class: |
C04B 40/00 20130101;
B01F 29/4033 20220101; B29L 2031/3412 20130101; B29B 7/842
20130101; B29C 48/295 20190201; B29B 15/08 20130101; B29C 48/29
20190201; B29C 70/025 20130101; B29C 37/006 20130101; B01F 29/60
20220101; H01B 19/00 20130101; B29C 70/48 20130101; B29C 48/08
20190201; B29B 7/106 20130101; B01F 35/7548 20220101; B29B 7/847
20130101; B01F 29/4034 20220101; B29C 67/244 20130101; B29K
2105/0005 20130101; B29C 67/242 20130101; C04B 40/00 20130101; C04B
26/02 20130101; C04B 40/00 20130101; C04B 28/00 20130101 |
Class at
Publication: |
524/494 ;
264/240; 264/255; 264/257; 264/102; 65/476; 34/443 |
International
Class: |
C08J 005/06 |
Claims
What is claimed is:
1. A method for producing at least a two primary phase compound
material substantially free of air and other gases by separate
treatment of the solid primary phase and the liquid primary phase
prior to bringing them in contact at mixing.
2. A method for producing at least a two primary phase compound
material substantially free of air and other gases comprising the
steps of: washing a primary solid phase with a condensable gas, so
as to substantially remove and replace void contents; mixing said
primary solid phase with a primary solidifiable liquid phase so
that the said two phases and only said condensable gas phase are
present in a mixed state; and condensing said condensable gas phase
such that it liquifies in said mixed state such that said
solidifiable compound comprises at least said solid phase and said
solidifiable liquid phase.
3. The method of claim 2, wherein said washing step comprises the
step of streaming said condensable gas through said primary solid
phase prior to said mixing step.
4. The method of claim 2, further comprising the steps of: placing
the two primary phase solidifiable compound in a solidifying
device; and solidifying said two primary phase solidifiable
compound so as to produce a composite material substantially free
of voids.
5. The method of claim 4, wherein said composite material is
substantially free of voids in that there are substantially no
visible voids of about 1 micron at about 1250.times. magnification
in any random sample of said composite material of at least 400
mm.sup.2 area.
6. The method of claim 2, wherein said solid phase comprises
particulate materials.
7. The method of claim 2, wherein said solid phase comprises
fibrous materials.
8. The method of claim 2, wherein said solid phase comprises any
combination of particulate and fibrous materials.
9. The method of claim 2, wherein said washing step is carried out
in a batch process prior to said mixing step.
10. The method of claim 2, wherein said washing step is carried out
in continuous process prior to said mixing step.
11. The method of claim 2, wherein said washing step is carried out
by any continuous or batch process, or any combination of said
processes, such that air and other gases are replaced by a
condensable gas prior to said mixing step.
12. The method of claim 2, wherein said mixing step is carried out
in a batch process.
13. The method of claim 2, wherein said mixing step is carried out
in a continuous process.
14. The method of claim 2, wherein said mixing is carried out by
any continuous or batch process, or any combination of said
processes.
15. The method of claim 2, further comprising the step of storing
said two primary phase solidifiable compound in which the gaseous
phase present is substantially condensable gas.
16. A solidifiable compound material in mixed state, comprising: at
least one primary solid phase; at least one primary solidifiable
liquid phase at least, in part, solidifiable; and at least one gas
phase comprising substantially a condensable gas; said solidifiable
compound when solidified becomes a substantially void free
composite.
17. The material of claim 16, wherein said condensable gas is
condensed prior to or at solidification of said compound.
18. The material of claim 16, wherein the primary liquid phase is
substantially completely solidifiable.
19. The material of claim 16, wherein the condensable gas comprises
at least one substance normally in liquid state at process
temperature and below 50 atmosphere pressure.
20. The material of claim 16, wherein the solidifiable compound
comprises the two primary phases and the condensable gas.
21. The material of claim 16, wherein the solidifiable compound
comprises two primary phases with any combination of condensable
gas and condensed gas.
22. An apparatus for the continuous and substantially void-free
production of a two primary phase solidifiable compound,
comprising: an enclosed container for a solid primary phase; a
vacuum applied to said container for said primary solid phase; a
continuous two primary phase mixing device in communication with
said enclosed container for receiving said primary solid phase; an
inlet for a condensable gas communicating with said enclosed
container in the initial region of said mixing device, so that said
condensable gas is a continuous counterflow stream with the flow of
said primary solid phase in said enclosed container; and a primary
liquid phase inlet communicating with said enclosed container and
downstream of said condensable gas inlet; said mixing device
continuously mixing and at least, in part, condensing said
condensable gas.
23. The apparatus of claim 22 further comprising a discharge port
for said solidifiable compound substantially free of air and other
gases.
24. An electrical insulator, comprising: a body with at least one
electrical contact; and said body constructed from a polymer
concrete composite material substantially void free and not having
visible voids of about 1.0 micron at about 1250 times magnification
and, said body formed by machining.
25. Any structural shaped product, comprising: a product with a
given shape; and said product constituted from a polymer concrete
substantially void free not having visible voids of 1.0 micron at
1250 times magnification.
26. Any dielectric shaped product, comprising a product with a
given shape; and said product constituted from a polymer concrete
substantially void free not having visible voids of 1 micron at
1250.times. magnification.
27. An apparatus for the batch and substantially void-free
production of a solidifiable polymer concrete material, comprising:
an enclosed mixing chamber; an enclosed molding chamber; and an
enclosed conduit communicating said mixing chamber with said
molding chamber; said apparatus being rotatable to cause the
contents of said mixing chamber to flow by gravity into said
molding chamber.
28. The apparatus of claim 26, wherein said apparatus is rotatable
about both a longitudinal axis and a transverse axis.
29. An apparatus for batch production of a two primary phase
solidifiable compound substantially free of air and other gases and
voids, comprising: a closed revolving chamber for containing and
mixing a solid primary phase, a primary solidifiable liquid phase
and a condensable gas; a source of vacuum applied to said chamber;
a source of pressure applied to said chamber; and a mold attached
to the discharge of said chamber.
30. The apparatus of claim 29, wherein the mold is detachable from
the closed chamber.
31. The apparatus of claim 28, wherein said enclosed molding
chamber of said apparatus is interchangeable with a material
holding hopper equipped with a intermittent dispensing device for
discharging discrete amounts of solidifiable polymer concrete
material from the apparatus.
32. The apparatus of claim 29, wherein the two primary phase
solidifiable compound with condensable gas is placed in the mold in
an air-free manner.
33. The apparatus of claim 32, further comprising a source of
pressure to condense the condensable gas in the mold.
34. The apparatus of claim 33, wherein said solidifiable compound
can be solidified in the mold.
35. The apparatus of claim 30, wherein the condensable gas is
vaporized from a gasifiable liquid placed inside the revolving
chamber with the primary solid phase.
36. The apparatus of claim 29, further comprising a manifold
discharge for unloading the solidifiable compound in mixed state
with condensable gas into one or more attached molds.
37. The apparatus of claim 22, wherein the discharge of the two
primary phase solidifiable compound is through an airtight,
expandable spout enabling intermittent discharges of discrete
amounts of said characterized compound in air-free conditions while
the mixing apparatus is running continuously.
38. The apparatus of claim 29, wherein said chamber revolves about
a longitudinal axis for mixing.
39. The apparatus of claim 29, wherein said apparatus rotates about
a transverse axis for material handling.
40. A method of removing air and other voids from a solid material
adapted for use in the production of void-free compounds,
comprising the step of: surrounding said solid material with a
condensable gas in an enclosed air-free environment to replace said
air and other voids with said condensable gas.
41. The method of claim 40, further comprising the step of mixing
said solid material with a solidifiable liquid phase to form a
two-phase solidifiable compound existing substantially solely in
the presence of said condensable gas.
42. The method of claim 41, wherein the solidifiable liquid phase
comprises a thermoplastic polymeric resin system.
43. The method of claim 41, wherein the solidifiable liquid phase
comprises a thermosetting polymeric resin system.
44. The method of claim 41, wherein the solidifiable liquid phase
comprises any combination of thermosetting and thermoplastic
polymeric resin systems.
45. The method of claim 41, wherein the solidifiable liquid phase
comprises an inorganic bonding system.
46. The method of claim 41, further comprising the step of storing
said solidifiable void-free compound in an airtight container.
47. The method of claim 41, further comprising the step of
condensing said condensable gas.
48. The method of claim 47, further comprising the step of
solidifying said compound under pressure or temperature, or any
combination of the two.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to gas occlusion-free and
void-free, two-primary phase, solidifiable compounds, and derived
void-free solidified composite materials, and more particularly to
gas occlusion-free and void-free polymeric solidifiable compounds
and derived void-free solidified composites, including methods and
apparatus for producing same.
[0003] 2. Description of Related Art
[0004] a. Terminology
[0005] Because certain terms in the field of the invention may be
used in different ways to signify the same or slightly differing
concepts, the following definitions are provided to promote clarity
for the following description of the invention.
[0006] The term "primary solid phase" is defined herein as one or
more distinct solid substances each physically homogeneous, in
solid state, which serves primarily as material reinforcement upon
solidification of the primary liquid phase.
[0007] The term "primary solidifiable liquid phase" is defined
herein as one or more distinct liquid substances, each physically
homogeneous, in liquid state, capable of solidifying to constitute
a solid continuous material matrix that binds the primary solid
phase at ambient temperatures.
[0008] The term "compound" is defined as the unsolidified state of
a composite.
[0009] The term "composite" is defined here as any solid primary
phase mixed with any primary solidifiable liquid phase, forming a
monolithic two-phase solid state material upon solidification of
the liquid primary phase.
[0010] When the two primary phases are mixed to yield a compound,
these primary phases are no longer in their primary state but in an
unsolidified, multiphase, "mixed state" as defined herein.
[0011] The term "voids" are defined herein as filled or unfilled
spaces, within interstices of a packed primary solid phase or
surface pores in solid constituents. Voids are further defined as
gas phase occlusions within a primary liquid phase originating from
entrainment and/or adsorption of air, water vapor and other gases
within the interstices of the solids in the primary solid phase,
within the primary solidifiable liquid phase or within the
multiphase, mixed unsolidified state of the two phases. The term
"voids", as defined above, specifically excludes intermolecular and
atomic spaces, which are natural unfilled spaces in matter.
Furthermore, the scale of physical measurement of voids herein is
about one micron (10.sup.-6 m) or more.
[0012] b. Polymeric Compounds and Composites
[0013] An extremely wide range of products are being manufactured
today from a specific class of two primary phase compounds in which
the primary solidifiable liquid phase is a polymeric resin. The
process leading to the production of a polymeric composite involves
mixing a generic primary solid phase with a polymeric resin system,
thereby constituting a two-phase unsolidified compound. Upon
further processing, the polymeric resin in the mixed unsolidified
state is made to solidify, or harden, in an appropriate forming
device, such as a mold or a die, yielding a formed, solid composite
with the shape, or configuration, of the forming device.
[0014] The role of the polymeric liquid resin system in polymeric
composites is to provide an essential binding matrix to the primary
solid phase upon solidification. Initially, its low viscosity
provides an adequate liquid medium for mixing with the solids of
the primary solid phase. Upon solidification, the resin matrix
provides a continuous solid phase that enables the composite to
behave monolithically as a single solid material body.
[0015] Resin systems in polymeric composites are further classified
as either thermoplastic, which soften when heated and may be shaped
or reshaped while in a semifluid state or thermosetting, which are
generally low viscosity liquids that solidify through chemical
cross-linking. The most common resin systems in polymeric
composites are thermosetting, and the most predominant
thermosetting resin is unsaturated polyester. Other thermosetting
resins include epoxies, vinylesters, phenolics and urethanes.
[0016] Certain thermosetting polymer resin systems consist of solid
polymer particles dissolved in a low viscosity liquid and solvent
monomer, for example, an unsaturated polyester dissolved in
monostyrene. The monomer plays the dual role of providing a solvent
medium for the distribution of the polymer resin, and also has the
ability to react with the polymer into a final solid state. Such
thermosetting resin systems are made to harden or solidify into a
permanent shape by an irreversible chemical reaction known as
curing or cross-linking, in which linear polymer chains and monomer
chains in the liquid resin system are joined, or reacted, together
to form complex, highly rigid, three-dimensional solid structures.
This reaction requires anaerobic conditions; i.e., the liquid resin
system will not harden in the presence of air. Thus the presence of
O.sub.2 is known to have an inhibitory effect on the
polymerization/solidification process. Additionally, water, which
is known to diffuse into liquid thermosetting resin systems,
significantly impairs the cross linking solidification
reaction.
[0017] An additional property of thermosets is that they are
generally brittle. Thus, thermosets are rarely used without some
form of solid reinforcement. However, high resistance to weight
ratio, ability to solidify at ambient temperatures and retain their
shape and properties at somewhat elevated temperature as, well as
good creep resistance and corrosion resistance properties, give
thermoset resin systems significant advantages over thermoplastics.
These advantages essentially are the reasons for their preference
in the developmental history of polymeric composites.
[0018] The role played by the solids in the primary solid phase
matrix of polymeric composites is one of structural reinforcement.
Moreover, the choice of geometrical shape of the solid phase
constituents is a function of the intended reinforcement
requirement of the particular polymeric composite in terms of the
type of predominant stresses from externally applied forces that
are to be resisted. The geometrical shape of the solid
reinforcement generally can be of two generic classes: 1) filament
shaped, or fiber and 2) granular/spherical shaped, or
aggregate-type solid material. The fiber reinforced polymeric
composites are intended for predominantly tensional, mechanical
resistance applications, whereas the aggregate reinforced polymeric
composites are intended for predominantly compressional, mechanical
resistance applications. These generic classes of solids can be
viewed as forming two ends of the structural resistance spectrum of
polymeric composites.
[0019] Polymer composites composed of fibrous solid materials mixed
with thermosetting polymeric resin are known as "Fiber Reinforced
Polymers" or FRPs. The most common fibers used in the present art
are glass, graphite, ceramic and polymeric fibers. Depending on the
particular production process used, this generic class includes
polymeric composite materials such as "Glass Reinforced Plastics"
(GRP), produced by open, manual or spray, lay up methods,
pultrusion, filament winding, etc. or by enclosed methods such as
"Resin Transfer Molding" (RTM), Seeman Composites Resin Infusion
Manufacturing Process (SCRIMP), etc. Other FRP composites produced
by enclosed methods are based on polymeric compound materials, such
as "Bulk Molding Compound" (BMC), "Sheet Molding Compound" (SMC),
"Thick Molding Compound" (TMC), etc. In the mixed solidifiable
compound state, the latter fiber reinforced polymeric materials,
appropriately handled, can be stored for extended periods of time
for future forming and curing at appropriate combinations of
pressure and temperature into final solid composite products.
[0020] Solid aggregate materials mixed with thermosetting polymeric
resin (resins) matrices comprise the generic class of polymeric
composites known as cast polymer products, polymer concretes,
polymer mortars or polymer grouts. To date, the inorganic
aggregates for polymeric composites have not been systematically
characterized, but most common aggregates used in the present art
are siliceous. Silica aggregates are widely used in the production
of polymer concretes due to their mechanical, dielectric and
chemical resistance properties, as well as for their abundance and
low cost.
[0021] Thermosetting polymeric composites offer inherent advantages
over traditional materials (metals, cement concrete, wood, ceramics
and natural inorganic materials), including energy efficiency, high
strength-to-weight ratio, design flexibility, parts consolidation,
corrosion resistance, high dielectric and thermal properties,
excellent appearance, low maintenance and extended service life. A
vast array of thermosetting polymeric composite products are
currently available worldwide in over 50,000 successful
applications developed over the past 45 years. Well over 95% of the
U.S. production is dedicated to fiber reinforced polymeric
composites, and the industry's shipments and growth are tracked
under nine major market segments totaling over 3.2 billion pounds
per year. Aggregate polymeric composites are widely used as cast
materials for bath tubs, shower stalls, kitchen sinks and counters,
flooring and decorative panels in construction. Cast polymer
concrete products find use in specialized niche industrial
applications, where the combination of high structural strength,
corrosion and dielectric resistance is required.
[0022] Despite some differences, these two generic classes of
polymeric composites have much in common in terms of certain
characteristics and general behavior. Generally, the functional
concepts and behavioral aspects of the polymeric resin systems are
the same for both classes of generic composites, despite specific
differences in the properties and geometries of the solids within
each class. Key common and inherent characteristics of polymeric
composites include: 1) the composites are all heterogeneous and
most are anisotropic; 2) the composites generally exhibit
considerable variability in their properties compared to metals;
this variability is directly related to the volume of the
respective fractions of the two phases, i.e., the primary liquid
phase versus the primary solid phase; and 3) the composites follow
a general "rule of mixtures," in which a property of the composite
is equal to the sum of solid and resin matrix properties weighted
by their respective volume fractions. The rule of mixtures,
however, is not valid for most properties in fiber reinforced
polymeric composites, except for longitudinal extensional modulus.
In aggregate reinforced polymeric composites, the correlation of
properties determined by the "rule of mixtures" is reasonably valid
for many properties and supports the art of solid filler additives,
commonly used to enhance desired properties in the composite,
and/or mitigate the effects of undesired properties.
[0023] Heterogeneity in a two-phase polymeric composite material
refers to certain properties that vary from point-to-point
throughout the mass of the material. In a random selection of a
point inside the material, properties can be very different,
depending on whether the chosen point falls in the polymeric matrix
or in the solid component. While it is true that generally all
composite materials are heterogeneous at the micron level, the
degree of heterogeneity is generally more pronounced in fiber
polymeric composites.
[0024] Additionally, the heterogeneity of these materials
contributes to the significant variability of properties of
thermosetting polymeric composites. In the case of FRPs, properties
depend on the combination of several factors, such as the
properties of the constituents, the form of the fiber reinforcement
used (continuous fibers, woven fibers, chopped fibers, etc.), fiber
volume fraction, length, distribution and orientation, bond
strength between the phases, and void content. For example,
strength and hardness characteristics of FRPs with continuous
length fibers depend strongly on fiber orientation, spatial
distribution and the variability of the properties of the specific
fiber chosen. As it is impossible to position each fiber
individually in the mix, the variability of the properties of the
material is inevitable. The variability of composites reinforced
with discontinuous fibers, such as bulk molding compounds (BMC) and
sheet molding compounds (SMC) which are ultimately shape-molded and
cured in closed dies, is even more enhanced due to the difficulty
in controlling local uniformity of fiber content and orientation in
the face of material flow. Accordingly, material hardness and
strength in the finished fiber reinforced composites made of BMC or
SMC may vary considerably from point-to-point throughout the
material.
[0025] Anisotropy is another characteristic common to thermosetting
polymeric composites, and is generally more pronounced in fiber
polymeric composites than in aggregate polymeric composites. An
anisotropic material is one whose properties vary with direction.
In the case of FRPs with straight, parallel and continuous fibers,
the strength of the material is significantly stronger and stiffer
in the direction parallel to the fibers than in the transverse
direction.
[0026] Reinforcing fibers used in fiber polymeric composites are
man-made in continuous processes yielding fine filaments that are
quite brittle, and generally consisting of diameters ranging from 2
to 13 microns. Filaments are normally in bundles of several strands
as rovings or woven into fabrics. Glass fibers are the oldest,
cheapest and most widely used. They have generally good chemical
resistance, are noncombustible and do not adsorb water, although
generally they adsorb humidity from air in atmospheric conditions.
Their tensile strength-to-weight ratios are relatively high, with
elastic moduli in the range of those of aluminum alloys. The
internal structure of glass fibers is amorphous, i.e.,
noncrystaline, and are generally considered isotropic.
[0027] Reinforcing aggregates used in aggregate polymeric
composites are natural occurring inorganic materials that require
processing to remove undesirable contaminants, such as clays, iron
oxides, etc. This processing involves mechanically sieving the
granules, separating them by sizes, and drying them within 0.1%
humidity by weight to assure compatibility with the resin systems.
Humidity strongly affects interfacial bonding of the resin with a
dramatic drop in compression and flexure strengths. Geological
origin, impurity levels, particle size distribution, and particle
shape all affect uniformity and homogeneity of dispersion of the
aggregates in the liquid resin system. These factors influence, in
turn, interfacial bond strength and void content. For high
corrosion resistance, thoroughly washed and dried, high silica
content aggregates are generally used. Rounded, spherical-shape
aggregates generally provide better mechanical and physical
properties than crushed, angular-edged aggregates, and also yield
higher packing aggregate fractions with reduced void content and
reduced resin fraction volume.
[0028] C. Voids in Polymeric Compounds and Composites
[0029] Voids are a major factor significantly contributing to
property variation within a polymeric composite. Voids tend to
reduce the integrity of the material and its mechanical and
dielectric strengths, cause optical defects and lower the chemical
resistance.
[0030] Any open space or volume in the surface of solid matter, or
the interstices of fractured packed solids, exposed to atmosphere
are subject to atmospheric air pressure, which will instantaneously
fill these spaces with air. For example, when solid silica is
fragmented and packed, as in the case of silica aggregates for
polymeric concretes, or when filaments of molten silica glass are
packed together to form glass fiber, as in the case of fiberglass,
the mass of the fragmented packed aggregates or packed filaments
exhibit an "apparent or bulk density" which is significantly lower
than the respective unfragmented or unfilamented specific density
of the respective original solid materials. For example, silica has
a specific density of 2.65 g/cm.sup.3 whereas the same silica
fragmented into small diameter particles, approximately from say
100 microns up to say 6 mm, has a "bulk" density of only 1.6
g/cm.sup.3. This "bulk density" indicates that the silica particles
of irregular geometries in contact with each other, as when packed
in a heap, leave random dimensional interstices or spaces--voids
that are filled with air. Neglecting the weight of air, the sum of
voids in one cubic centimeter of particulated silica is equivalent
to the volume occupied by 1.05 grams of solid silica; that is,
39.6% of the fragmented silica volume corresponds to "air in the
voids within the silica heap."
[0031] Since the formulations of polymeric composites are normally
gravimetric, or by weight of bulk solids and liquid fractions, and
furthermore, since the entrapped air is of negligible weight, its
presence is not recognized gravimetrically. However, as detailed
above, the properties of polymeric composites are related primarily
to volumes of the constituent solid and liquid phase fractions,
which, of course, include whatever volumes are actually occupied by
air and water vapor entrapped in void spaces of fragmented or
filamented solids. Moreover, the air, water vapor and other gases
entrained in the voids of the solids add an important contribution
to the total volume of the mixed compound material when the
original solids are mixed with the liquid polymeric resin system.
In fact, it is important to recognize that at the start of mixing
of the two primary phase polymeric compound, actually three phases
are present: (1) the original primary solid phase, (2) the original
primary solidifiable liquid phase (e.g., a polymeric resin system),
plus (3) a gaseous phase made up of the entrained air, water vapor
and other gases in the primary solid phase, plus entrained air,
water vapor and other gases that may be dispersed in the resin
system. Moreover, interfacially active substances generally added
in the resin manufacture stabilize air inclusions.
[0032] The presence of voids in a solid composite material
interferes with its integrity because voids randomly interrupt the
continuity, not only of the primary solidified liquid phase, but
more importantly, also the continuity of the interfacial bond
between the primary phases. Void sizes, number, distribution, and
especially, locations are all critical because voids determine
singular points of discontinuity within the phases of the material.
These discontinuities compromise the composite's integrity,
strength, and further, lead to the initiation of failures due to
the localized stress concentration points they create. Moreover, if
these voids in the mixed unsolidified state are filled with air and
water vapor, O.sub.2 in air will cause an inhibitory effect on the
polymerization reaction of the resin. Water, particularly in liquid
state, can be even more detrimental than O.sub.2 to the
polymerization reaction and to solidification. Thus, the removal of
air, water vapor and other gases from the primary liquid resin
system can result in more complete polymerization/solidification of
the resin, thereby producing a material with greater strength and
integrity.
[0033] For example, in fiber reinforced polymer composites, voids
upset the rule of mixtures. Interlaminar shear strength should
increase with increasing fiber volume fraction content. Instead,
shear strength actually decreases, even at relatively low void
contents. Experiments show that a 5% void content causes a 35 to
40% drop in interlaminar shear strength in a fiber/epoxy composite.
(Delaware Composites Encyclopedia, Vol. 1, page 29, Technomics
Publishing Co. 1989). In many fiber reinforced composite
fabrication processes, void content tends to increase with
decreasing resin content, i.e., with increased solid content.
Again, it is notable that all strength properties of fiber
reinforced polymer composites drop off at higher fiber volume
fractions contents--generally above 50% fiber volume content,
contrary to the expectations of the rule of mixtures. A particular
study for E-glass/epoxy unidirectional composite made by filament
winding shows a reduction of 30% of linear fiber stress strength at
failure with an increase of fiber volume fraction from 60% to 70%.
(Delaware Composites Encyclopedia, Vol. 1, page 66), Technomics
Publishing Co., 1989). On a weight basis, typically a 60% glass
fiber volume fraction is generally attained with machine processes
and represents 78% of total weight of the composite. The highest
reported glass fiber volume fraction content in non-machine
processed composites in the industry, such as in RTM or SCRIMP, is
generally about 70% by weight, which is equivalent to just 50% of
fiber content by volume.
[0034] In the case of aggregate polymeric composites, however,
strengths follow the rule of mixtures, and properties, particularly
compression strength, actually increase with increasing aggregate
volume fraction content (provided that the aggregate fraction's
particle size distribution is suitably graded for highest aggregate
volume packing). Moreover, this increase in mechanical properties
is observed in spite of the increased void content accompanying the
increased aggregate volume fraction. In this case, the increased
number of gas occlusions producing voids can be offset by
mechanical vibration and vacuum of the mix, resulting in a somewhat
degassed mix. Notwithstanding this fact, random voids remaining in
aggregate polymeric composites also constitute points of stress
concentration which are detrimental to mechanical strength
properties of the material and contribute significantly to the
variability of properties exhibited by the final composite
materials.
[0035] E. Degassing Devices
[0036] The present state of the art attempts to deal with the
removal of the entrained gaseous phase after the mixing the two
primary phases. To deal with gas occlusions, conventional
fabrication processes of polymeric composites generally require
that the viscous compound mix, with or without special air release
additives, be degassed under vacuum and/or pressurized and, in some
cases, also mechanically agitated, vibrated, compacted, or
combinations thereof. The application of these process steps
enables movement of the gaseous phase within the viscous liquid mix
assisting it to migrate towards the external surfaces of the liquid
mass, escaping outside into the surrounding space. The freed gases
then can be extracted by vacuum. Essentially, in the prior art, the
gaseous phase is brought into the mixture entrained by the solids
and/or by the liquid resin system and gets dispersed into the mixed
unsolidified state. Therefore, in order to allow complete wet-out
of the solids by the liquid resin system, some mechanism for
removal of the gaseous phase is required. This is generally
accomplished by degassing thin films of the mix under vacuum, which
allows the occluded gas bubbles within the thin section to move
towards its external surface. Moreover, these external surfaces are
maintained at a lower pressure than the thin mass itself, thus
facilitating evacuation by vacuum.
[0037] Present state of the art phase-mixing processes used to
process polymeric composites, however, are not designed, nor
intended, to eliminate entrained air, water vapor and other gases
in the solids and liquid phases prior to the mixing process.
Generally, the prior art methods of degassing are designed to work
with the untreated primary phases already in the mixed state.
Evacuation of gases from the mix is not only more inefficient and
difficult but also less effective. Moreover, the mix can only be
partially evacuated through mechanical and vacuum methods. Thus,
the presence of voids in the final composite is inevitable using
prior art methods.
[0038] For example, application of vacuum in a fiber polymeric
composite made in a typical RTM or SCRIMP process does diminish
entrapped air within the closed mold, or system, and from the glass
fiber materials. Also gas vapors from the constituents of the resin
system or from entrained air can be diminished by the application
of vacuum, as evidenced by the reduction of visible occlusions in
the solidified two-phase material. Likewise, vacuum applied to the
thin sections of aggregate polymeric compounds in mixed state,
especially in conjunction with mechanical vibration, which allows
entrained air to be dislodged, and with air release additives that
reduce interfacial tension, diminishes the total entrapped air and
gases, and consequently, substantially diminishes occlusions/voids
in the solidified two-phase material.
[0039] In particular cases, such as aggregate polymeric compounds
involving resin/small diameter particulate microfiller mixtures,
degassing a thin film of this mix with high vacuum, as described in
U.S. Pat. No. 5,534,047, results in substantial elimination of
gases from the mix and accordingly, a substantially "void free"
composite is obtained. The success of this method is largely due to
the microsize range of the filler in the primary solid phase and to
relatively high resin matrix fraction volume of low viscosity,
which allow good homogeneous dispersion of the solids in the liquid
resin matrix. In this case, the primary solidifiable liquid phase
resembles a low viscosity liquid, and therefore, behaves more like
a pure liquid system. However, degassing by thin film vacuum as
suggested in U.S. Pat. No. 5,534,047, is limited to a narrow range
of applications. These applications involve either low viscosity
liquids or low or moderate viscosity solid/liquid mixes that are
capable of uniform gravity flow as thin films over flat surfaces,
and that allow for relatively unimpeded movement of entrained gas
occlusions by pressure differential through the viscous liquid
film. Generally, however, in the prior art, two primary phase
polymeric compounds are known to be incapable of being completely
degassed by conventional methods including high vacuum.
[0040] F. Conclusion
[0041] Overall then, it appears that conventional processes as
practiced in the present art of producing polymeric compounds
cannot completely eliminate gas occlusions and voids from the
compounds, and accordingly, from the corresponding solidified
composites thus obtained from them. Polymeric composites produced
in the prior art, therefore exhibit, high variability as well as
decreased mechanical and physical properties as compared with the
expected capabilities and performance of final composites produced
ideally void free Moreover, the apparent acceptance in the
composites industry of the presence of voids as unavoidable in the
production of polymeric composite materials has precluded their
potential cost effective penetration into new more technically
demanding applications.
[0042] Polymeric resin system materials cost is one of the major
factors affecting overall composite costs. Efforts to decrease
resin system cost for increased composites competitiveness in
market penetration have been generally frustrated because
associated increases in solid content generally worsen rather than
improve mechanical, physical and chemical properties, while
significantly increasing production difficulty.
[0043] Thus, there exists a need to produce polymeric
composites--both in fiber and aggregate classes--meeting a stricter
and more rigorous criterion regarding freedom from gas occlusions
and voids. If void-free, two-phase solid polymeric composite
materials can be readily produced, they will at least exhibit
increased mechanical, chemical resistance and physical strength,
decreased variability of properties and enhanced reliability and
performance. Polymeric composites in such a void-free solid state
condition would both lower costs and improve quality in existing
applications and thus, enable cost effective access to new, more
demanding applications.
SUMMARY OF THE INVENTION
[0044] The present invention comprises a method for producing at
least a two primary phase compound that is substantially free of
air and other gases by separately treating the solid primary phase
and the liquid primary phase prior to bringing the two phases into
contact. Treatment of the two phases entails washing the primary
solid phase with a condensable gas, so as to substantially remove
and replace the solid phase's void contents; and separately
degassing the primary solidifiable liquid phase by conventional
means. Once treated, the primary solid phase (whose voids are
substantially filled with the condensable gas) and the primary
solidifiable liquid phase, are combined in a mixing step, and the
condensable gas is condensed or liquefied in the mixed state. The
resulting void-free, solidifiable compound thus comprises at least
a solid phase and a solidifiable liquid phase. The solid primary
phase may consist of either particulate or fibrous materials or
combinations of both. The primary solidifiable liquid phase may
consist of a thermoplastic polymeric resin system, a thermosetting
polymeric resin system, a combination of both systems, or an
inorganic binding system. Further, both the washing and mixing
steps may be carried out in a batch or continuous mode, or in a
combination batch-continuous mode. Additionally, the two primary
phase solidifiable compound having a gas phase composed
substantially of the condensable gas may be stored for later
use.
[0045] The present invention also includes two primary phase
solidifiable compounds made in accordance with the inventive
method, as well as substantially void free polymeric composites
formed from the solidifiable compounds. Note, the condensable gas
that is used to wash the primary solid phase in the inventive
method, may be condensed prior to or at solidification of the two
phase compound, and may be partially or completely condensed in the
mixed state. Void-free composites made from the inventive method
are especially useful as electrical insulators.
[0046] The present invention also includes an apparatus for
continuous production of the substantially void-free, two primary
phase solidifiable compound. The apparatus is comprised of an
enclosed container for the primary solid phase, and a means for
producing vacuum within the enclosed container; a mixing device
that is in communication with the enclosed container, and that is
used both to combine the separately treated primary solid phase and
the primary solidifiable liquid phase, and at least partially, to
condense the condensable gas. The apparatus also comprises a
condensable gas inlet in the initial region of the mixing device,
so that the condensable gas flows continuously within the enclosed
container in a direction counter to the flow of the primary solid
phase; and a primary solidifiable liquid phase inlet located
downstream of the condensable gas inlet within the mixing device.
Finally, the apparatus contains a port for discharging the mixed,
and substantially air-free, solidifiable compound. Optionally, the
discharge port may consist of an airtight, expandable spout that
allows for intermittent discharge of discrete amounts of the
air-free compound while the mixing device continues to run.
[0047] Additionally, the invention includes an apparatus for batch
production of a two primary phase solidifiable compound that is
substantially free of air and other gases and voids. The apparatus
is comprised of a closed revolving chamber for containing and
mixing the primary solid phase, the primary solidifiable liquid
phase, and the condensable gas phase; a means for applying vacuum
and pressure within the chamber; one or more ports for discharging
the chamber contents; and fixed or detachable molds that are
attached to the discharge ports and are used to form the solidified
composite. In addition to rotation about its longitudinal axis, the
apparatus may also rotate about a transverse axis to aid in
material handling.
[0048] Finally, the invention encompasses an apparatus for batch
production of a substantially void-free solidifiable polymer
concrete material. The apparatus is comprised of an enclosed mixing
chamber, an enclosed molding chamber, and an enclosed conduit that
provides for communication of the mixing chamber with the molding
chamber. Moreover, the apparatus can be rotated in a vertical plane
about an axis perpendicular to the longitudinal axis of the
apparatus. This allows the contents of the mixing chamber to flow
by gravity into the molding chamber. The apparatus may also provide
a means for rotation about its longitudinal axis to mix the polymer
concrete components. The apparatus may also contain a material
holding hopper that can be interchanged with the molding chamber.
This hopper is equipped with an intermittent dispensing device that
provides for discharge of discrete and metered amounts of the
solidifiable polymer concrete material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] FIG. 1 is a schematic diagram illustrating the generic
method of the present invention for processing a generic void-free,
gas occlusion-free two primary phase solidifiable compound
material.
[0050] FIG. 2 is an illustration of some of the forms of voids.
[0051] FIG. 3 is a schematic representation of another application
of the present method in which a void-free polymer concrete
composite material is produced by a batch mix and molding
method.
[0052] FIG. 4 is a schematic representation of yet another
application of the present method in which a void-free polymer
concrete compound is produced by a conventional continuous mixing
method, and where a polymer concrete composite is produced by a
mixer to storage to mold method.
[0053] FIG. 5 is a schematic representation of still another
application of the present method in which a void-free fiber
reinforced polymer composite is produced by a Resin Transfer
Molding (RTM) method.
[0054] FIG. 6 is a schematic diagram of an apparatus of the present
invention, used in this case to produce a batch mixed polymer
concrete material, as illustrated in FIG. 3.
[0055] FIG. 7 is a schematic diagram of another apparatus of the
present invention used, in this case, to continuously produce a
void-free polymer concrete material, as illustrated in FIG. 4.
[0056] FIG. 8 is a schematic representation of an electric
insulator machined from a void-free polymer concrete composite
material produced according to FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0057] The present invention relates to methods, materials and
apparatus used to produce a variety of void-free materials. These
void-free materials, and the methods and apparatus for producing
same are also detailed herein. The generic void-free method can be
used to produce any two primary phase solidifiable compound and
composite.
[0058] A key step in this inventive method is to replace the
pre-existing entrained or entrapped gases with a selected
"condensable gas" as defined herein. The "condensable gas" utilized
in the present invention is defined herein as one or more
substances that at normal ambient temperature and up to 50
atmosphere of absolute pressure, exists as a liquid. The purpose of
the condensable gas in the invention is to displace and replace
air, water vapor and other gases present within the voids and
interstices of the primary solid phase. "Non-condensable gases" are
defined herein as air, water vapor and other gases, which
originally exist as gases filling the voids, and subsequently, are
replaced by a selected condensable gas. Thus, a "non-condensable
gas" is any gas other than the selected condensable gas used to
replace the pre-existing gases, or displaced gases, in the
system.
[0059] The present invention is an environmentally safe generic
process of universal application to fabricate all types of two
primary phase solidifiable compounds and composites, comprising a
primary phase of reinforcing solid mixed with a primary of
solidifiable liquid binder phase. It is applicable to the
production of void-free polymeric composites in general. In
particular, the method is applicable where the solidification
mechanism of the primary solidifiable liquid phase involves
solidification of its entire liquid phase. Additionally, the method
is particularly applicable where thermosetting polymeric resin
matrices are used as the primary solidifiable liquid phase.
Generic Method of Production
[0060] The generic method leading to void-free and gas occlusion
compounds involves three essential stages in the production
process. These stages are applicable to any method of production to
yield a wide variety of compounds and composites.
[0061] The state of the two primary phases in the generic process
are characterized in the invention at each of three successive
generic processing stages:
[0062] Stage 1--Washing the primary solid phase with a condensable
gas, in the gas or liquid state, and in parallel
de-airing/degassing the primary solidifiable liquid phase.
[0063] Stage 2--Mixing the above two primary phases, air-free, and
in presence of a condensable gas phase.
[0064] Stage 3--Condensing of the above condensable gas phase
within the mixed state compound.
[0065] Application of the above method yields a two-primary phase,
non-condensable gas occlusion free and void-free solidifiable mixed
state compound, which can be cured immediately or stored uncured
for future curing.
[0066] FIG. 1 shows a schematic of the generic process used to
produce a generic non-condensable gas occlusion free and void-free
two-primary phase solidifiable compound as disclosed in the present
invention. The initial steps 1 and 2, consist of separating the
primary solid and liquid phase for the purpose of independently
removing air, water vapor and other gases entrained in each phase
prior to mixing. As indicated, each primary phase contains
entrained non-condensable gases, which in the case of the primary
solid phase, are removed by the inventive method.
[0067] A. Stage I
[0068] An important step in the process is 5, shown in FIG. 1,
where the primary phase solids are de-aired/degassed by total
replacement with a condensable gas 4. This step 5 is significant to
produce a non-condensable gas occlusion free and void-free compound
because it permits the complete replacement of air/gases by washing
the solids with a condensable gas chosen to adequately work within
the parameters of conventional fabrication processes. The addition
of this step to the overall void-free method recognizes the fact
that it is essentially impossible to completely degas solids, or
mixtures of solids and liquids, using conventional techniques with
or without the application of vacuum. Thus, the present invention
replaces air, water vapor and other non-condensable gases entrained
in the solid with a condensable gas that can be liquefied within
the mixed unsolidified state compound in the range of temperatures
and pressures in which the production processes are carried out.
Ideally, the condensable gas utilized, when liquified, would be
reacted within the primary solidifiable liquid phase prior to, or
at, solidification to form a solid void-free composite in a
subsequent step.
[0069] As illustrated in 3, after washing the solids in a stream of
condensable gas, the displaced air with associated water vapor and
other gases can be removed by vacuum together with the stream of
condensable gas. With the application of vacuum, at this point in
step 5, the condensable gas in filling the voids in the solids as
the air associated with water vapor and other gases are being
removed, and the condensable gas is also simultaneously being fed
into the primary solid phase, as seen in 4.
[0070] The condensable gas as a liquid state substance is vaporized
to its gas state by some appropriate combination of pressure and
temperature. The preferred vaporization conditions are at ambient
temperature together with sufficient vacuum for vaporization. The
preferred choice of a condensable gas is one that in its condensed
liquid state would be capable of further reaction with the primary
solidifiable liquid phase upon its solidification. There are
essentially three classes of condensable gases disclosed in the
present invention. Class I uses one or more liquid substances
contained in, or forming part of, the solidifiable liquid system as
sources of condensable gas to wash the primary solid phase. Class
II uses one or more liquid substances, other than those forming
part of the solidifiable liquid system, as a source of condensable
gas to wash the primary solid phase. In the case of Class II, the
liquid substances are functionally equivalent to those contained in
Class I, in that Class II liquids are also capable of reacting in
the solidification, or curing, process. Class III substances do not
utilize a reactive or functionally equivalent fluid substance as a
source of the condensable gas, but instead uses one or more fluids
that are either soluble or insoluble in the solidifiable liquid
system process conditions. Thus, for example, where the primary
solidifiable liquid phase is an unsaturated polyester, styrene
monomer would serve as a Class I condensable gas. Furthermore,
other ethenic polymerization monomers could serve as Class II
condensable gases, including, acrylamide, methyl acrylate, methyl
methacrylate, vinyl acetate and the like. Finally, suitable Class
III condensable gases would be organic solvents having normal
boiling points between about 50.degree. C. and 100.degree. C.,
including acetone, methanol, ethanol, isopropanol, acetonitrile,
and the like.
[0071] Preparation of the substance to be used as condensable gas
in the invention can be done by methods generally known in the art,
which include evaporation of the gasifiable liquid into a
condensable gas with subsequent feeding of the gas thus produced
into a gas replacement chamber 5. Preferably for continuous
washing, evaporation of the gasifiable liquid may take place
outside of the gas-replacement chamber, and then fed into the gas
replacement chamber 5. Alternatively, preferably in the case of
batch processes, evaporation of the condensable gas can take place
within the gas replacement process chamber 5. In the case of Class
I Liquid/gases, one or more of the liquid substances from within
the solidifiable liquid system can be selectively evaporated from
it and fed into the gas replacement process chamber 5. In still
another alternative, evaporation into a condensable gas, using an
appropriate temperature and pressure, can take place outside the
gas replacement process and fed into it at elevated temperature, so
that it is made to condense inside the gas replacement process
chamber at process temperature and then subsequently re-evaporated
within chamber 5 by a combination of pressure and temperature.
[0072] In parallel, the present invention requires that the primary
liquid phase 2 be degassed by conventional vacuum methods,
preferably thin film vacuum methods. This step allows removal of
the entrapped air, water vapor or other gases within this primary
phase. The de-airing/degassing of the primary liquid phase takes
place in a degasifying process chamber 6. Reference numeral 7
illustrates that the air, water vapor or other gases entrained in
the primary liquid phase are removed by the application of thin
film vacuum methods which are generally more effective.
[0073] B. Stage II
[0074] Reference numeral 8 and 9, shown in FIG. 1, represents that
the two primary phases having been separately treated to remove
entrained air, water vapor and other non-condensable gases, and
now, being de-aired/degassed by conventional methods in the case of
the liquid phase, and condensable gas-replaced by washing with
condensable gas in the case of the primary solid phase, can proceed
to be mixed to form a non-condensable gas free, void-free
solidifiable compound. Reference numeral 10 represents the air-free
mixing processes into which each pretreated primary phase is
contacted to begin the mixing process of what is now a primary
solid phase, a primary solidifiable liquid phase and a condensable
gas system, to yield a mixed state non-condensable gas occlusion
free and void-free solidifiable compound. The mixing step 10 must
be conducted only in air-free conditions and with the presence of
the condensable gas in the gaseous phase.
[0075] The condensable gas in the mixing chamber may or may not be
uniformly dispersed in the solidifiable liquid phase. An optional
step can be performed at this point to disperse the condensable gas
more homogeneously within the solidifiable liquid phase. This
optional step can be accomplished by applying vibration or
mechanical work to the mixed state compound. Additionally, if
elimination of excess condensable gas is desired, as it might in
batch mixing process, vacuum and mechanical work can be applied at
this point to achieve this end.
[0076] C. Stage III
[0077] The next step is significant to the overall void-free
process and production of the non-condensable gas occlusion free
and void-free compound to yield a final void-free composite
material. This step involves condensation of the condensable gas
preferably within a condensation chamber 12, as shown in FIG. 1.
Later, at the time of forming and hardening of the compound,
pressure and/or heat can be applied to form a final solid
composite. This essential step 12 takes the condensable gas to its
corresponding liquid state at process temperature by application of
pressure 13, or by some appropriate combination of temperature and
pressure. Upon condensation of the condensable gas throughout the
mixed state solidifiable liquid system, all spaces in the mix
previously occupied by the condensable gas, as a gaseous state
substance, are available to be occupied by the solidifiable liquid
system which does so assisted by its own pressure, so the mixture
becomes a non-condensable gas occlusion free compound. Concurrent
with this essential condensation step, the solidifiable compound
may be vibrated or mechanically worked upon, as illustrated in 14,
so that the condensed gas, now in liquid state, may be dispersed
within the liquid phase of the mixture, thus allowing penetration
of the liquid phase into interstices and voids on the surfaces of
the solids. Alternatively, vibration need not be applied because
the element of time can be used to allow for diffusion of the
condensed gas liquid droplets within the liquid system as seem in
15. Reference numeral 16 represents the end product of the generic
process, yielding a non-condensable gas occlusion free, and
void-free, two primary phase solidifiable compound that can now be
immediately hardened or stored for future solidification.
[0078] The effectiveness of the method and mixing conditions
disclosed in the present invention, specifically, in terms of prior
displacement of air, water vapor and other gases from voids in the
dry solids by washing with a condensable gas and subsequent total
replacement with a condensable gas, cannot be attained by present
art vacuum only processes. The reason stems not only from the fact
that perfect vacuum conditions cannot be achieved, so the entrained
gases in the solids can only be rarefied at best, and moreover,
because total dependence on high vacuum to maintain an air-free
condition of the primary solid phase is unfeasible and impractical.
It is perhaps for this latter reason that vacuum degassing
pretreatment of the solids has not been considered in present art
nor included in conventional processes.
[0079] As stated above, in contrast to the present invention, the
typical prior art degassing processes shift all attempts of gas
removal to the wet mixing stage of the two primary phases. In that
case, the non-condensable gases naturally present in the mixing
process become dispersed throughout the mixed state compound mass,
making vacuum degassing at this stage ineffective and inefficient.
Again in contrast to the present invention, the prior art procedure
is considerably more difficult and less effective in high viscosity
systems. In fact, in the prior art methods, gas phase removal
becomes virtually impossible in cases where the resulting mixture
viscosity of the mixed state of the solid and liquid phases is
significantly increased by their addition.
Void-Free Considerations in Polymeric Compounds and Composites
[0080] It is somewhat surprising that current technical literature
on voids does not delve into the causes or origins of voids in
solid state polymeric composites, and no link has been established,
or suggested, to identify their origin as gas occlusions already
pre-existing in the original solidifiable--two phase mixed state
compound. Voids in the compound are then transported into the
solidified resin matrix of the composite. In developing the present
invention, it has been discovered that the success of any air-gas
phase removal strategy from the mass of a two primary phase mix
containing a gaseous phase depends on the following:
[0081] ratios or surface tensions existing between the gaseous,
liquid and solid phase present in the mix;
[0082] average size of the air and gas occlusions;
[0083] pressure differentials that can be established between those
within the different gas occlusions, and that of the external
surface of the mass maintained at a lower pressure;
[0084] viscosity and rheology of the liquid state mixture;
[0085] geometry of the specific masses;
[0086] length of the paths the occlusion gas bubbles need to move
to access the lower pressure external surfaces;
[0087] obstacles intercepting the paths of the occluded gas
bubbles;
[0088] ability of mechanical vibration applied to the mass to pack
the solids within the liquid for displacing gas occlusions;
[0089] time that the vacuum originating the pressure differential
is maintained.
[0090] Given that we are surrounded by air and atmospheric
pressure, the natural state of voids in open atmosphere is to be
filled with air, water vapor and other gases as defined herein.
Ideally, upon mixing the two primary phases into the unsolidified,
multiphase, mixed state, voids in the primary solid phase and in
the mixed unsolidified state should be completely occupied by the
solidifiable liquid phase. The occupation, however, is generally
precluded by the counter pressures exerted by the gases in gaseous
state filling the voids. Therefore, this gaseous phase filling
voids will be retained in the mixed, unsolidified state. Moreover,
if no effort is made for their elimination, the gas occlusions will
remain in the mixed state solidifiable compound, and thus, will
irremediably appear as voids in the final solid composite.
[0091] In the final solid composite, voids or unfilled spaces
within the solidified liquid phase may be generated by one or more
constituents materials of the mixed state gas occlusion free
solidifiable compound, or during subsequent storage, handling and
processing. Such voids in the solidified composite are not caused
by non-condensable gas filled voids or unfilled resin voids
pre-existing in the mixed state gas occlusion free solidifiable
compound, and thus the invention remains valid.
[0092] In the invention, the primary solidifiable liquid phase is a
polymeric resin system generally exhibiting typical viscosities at
normal process temperatures. These viscosities determine a behavior
of the gaseous phase that require further description. Gaseous
phase occlusions are suspended in the polymeric resin system
occurring naturally as discrete spherical volumes maintained by a
pressure and surface tension equilibrium that is established
between the liquid and gas phases. Also, gaseous phase occlusions
may occur as amorphous thin layer gas filled voids of large surface
to volume ratio, lodged in the interstices within fibers or formed
around closely packed aggregates in the primary solid phase upon
mixing with the polymer resin system, particularly in compounds
having high volume fraction of solids.
[0093] In the mixed unsolidified state, the voids in the primary
solid phase may release some of the entrained gaseous phase into
the primary liquid phase, where it may join other entrained gases
found in the primary liquid phase. Mechanical work applied to the
mixed state of the two primary phases containing entrained third
gaseous phase will generally help the release of the gaseous phase
lodged in voids of the primary solid phase into the primary liquid
phase and also help disperse the gaseous phase within the liquid
phase. Mechanical dispersion of the gaseous phase can also increase
the surface to volume ratio of the gas occlusions. Some gas
occlusions get broken down into smaller spherical sizes, while
others may adopt other than spherical shapes, generally of high
surface relative to their initial volume, such as the amorphous
thin layers voids described above. Gases filling these amorphous,
thin layer voids are completely entrapped in the interstices within
fibers or within packed fibers or aggregates by the surrounding
primary liquid phase, forming localized and enclosed micro-gaseous
phase systems separating the two primary phases in mixed state at
discrete locations. Moreover, the volumes of localized, enclosed
micro-gaseous phase systems will be determined by a pressure
equilibrium existing between the gaseous phase systems internal
pressure and the surrounding liquid phase at a given process
temperature. This pressure barrier prevents the surrounding liquid
phase from wetting out the interstices of the solids where the
micro-gaseous systems are lodged.
[0094] As indicated above, voids can take several typical forms
within the primary phase materials. FIG. 2 provides an illustration
of some typical void forms in solid primary phases, prior to
mixing. Voids can be viewed as spaces between the interstices of
packed solids of a primary phase, prior to mixing, as shown in 21
in aggregates, and as shown in 22 in fibers. The amorphous, high
surface to volume voids, in the form of thin layers of gas adsorbed
on the surface of solid in the mixed state are shown in 23 in an
aggregate/resin system, and in 24 in a unidirectional and random
oriented fiber/resin systems. Reference numeral 25 illustrates the
typical natural spherical gas bubble shape upon mixing of the
primary phases. The above characterized voids shown in 23, 24 and
25 are formed typically in the mixed state and will be retained in
the final composite material upon solidification, if no effort is
made for their removal.
[0095] The significant deleterious effect of even low void content,
with their associated air, water vapor and other non-condensable
gases, in fiber reinforced polymeric compounds in the mixed state
and carried over to the solid composite state are not generally
fully recognized. Voids remain one of the major unrecognized source
of problems fiber reinforced organic polymeric composites face
today. Specifically, amorphous thin gas layers randomly located
constitute a barrier intercepting contact of the fiber and liquid
phases, and thus significantly affect proper resin wet out. More
particularly, this barrier discretely interrupts the continuity of
interfacial bonding. For an illustration, consider a typical 9
micron fiber diameter fiber reinforced polymeric composite with a
1% void content by volume--a void level which is generally
considered acceptable by industrial quality standards. The effect
of that 1% void content, if present as random thin gaseous layers
of sub micron thickness on the fiber surfaces, as would be typical
in fiber reinforced composites manufactured through mechanical
work, could be interpreted as being equivalent to compromising, or
nullifying, the overall contribution to tensile strength at failure
of approximately 5 to 7% of the fiber volume fraction present in
the composite.
[0096] If no mechanical work is involved in the production of the
fiber reinforced compound, such as in RTM or SCRIMP, it is
reasonable to expect that more voids will be as gas occlusions
randomly suspended in the resin of the liquid phase, which
generally do not affect fiber wet out and interfacial bonding as
much as gas layers lodged within or around the fibers. Moreover,
also in this case resin volume fractions are generally higher, and
the overall fiber contribution nullified by voids would tend to be
less dramatic. However, there is a practical fiber volume fraction
limit in non-machine processed products in industry today, at
around 50% by volume. This is imposed not only by the generally
practical difficulty of achieving higher fiber volume fraction
packings, but also by the effects of voids at high fiber volume
fractions, forming amorphous thin layer gaseous random entrapments
of very high surface to volume ratios in the interstices of the
highly packed fiber arrangements. The counter pressures of such
voids prevent resin wet out of longitudinal contact surfaces of the
fibers and within fiber interstices. These gas occlusions cannot be
removed by the normal vacuum levels of RTM or SCRIMP processes, so
attempts to increase fiber volume fraction in these types of fiber
reinforced polymeric composites, unless voids are first eliminated
as per the invention, would not be productive.
[0097] The application of the general rule of mixtures to fiber
reinforced composites for longitudinal and transverse extensional
moduli suggests a linear increase of moduli with increasing fiber
volume fraction. However, as pointed out above, this is not
evidenced at high fiber volume fractions beyond 50%, where material
properties in fact actually decrease. Presumably, such anomalies
could be attributed to the deleterious effects of voids in the
fibers preventing proper fiber wet out and overall interfacial
bonding which is additionally severely affected by reduced levels
of available resin matrix content in high fiber volume fraction
compounds.
[0098] Therefore, unless void are first completely eliminated from
the mixed state compound, making accessible to the liquid resin all
available fiber contact surfaces, which will be otherwise partially
blocked by the voids, any increments of fiber volume fraction will
generally have the equivalent effect of nullifying several times
more fibers than are added.
[0099] It is impossible to control or predict with any accuracy the
forms or locations of entrained air, water vapor and other gases
from the primary phases forming voids in the mixed state of a two
phase polymeric compound. A wise strategy to improve maximum wet
out of the phases and obtain optimal interfacial bonding of the
surfaces of the total fiber available with resin is, prior to
mixing, to eliminate air/water vapor gases completely from the
fibers, and likewise, to completely degas the liquid resin phase
and eliminate its entrained air and other gases. Moreover, the
adoption of a rigorous elimination of voids in the production of
fiber reinforced polymer composites, particularly at higher fiber
volume contents, will facilitate increasing composite strength with
increasing fiber volume content, and thus approximate the composite
behavior to that expected by the rule of mixtures. An important
corollary of this is that at high fiber volume contents and
diminished resin volume contents, the ratio of fiber contact
surface to available resin volume increases and interfacial boding
becomes critical. In this case, overall strength appears foremost
related to actually achieving maximum successfully bonded surface
adhesions between the two primary phases rather than to the
particular resin strength properties themselves.
[0100] The present invention allows reaching a substantially
void-free condition. A non-condensable gas occlusion-free and
void-free material is defined as a two primary phase solidifiable
polymer compound when in substantially the liquid state, and as a
void-free composite when in the solid state. Polymer composites
made in accordance with present invention exhibit no gas occlusion
voids, in the size range of one micron visually detected under
1250.times. magnification in any random cross-section sample of at
least 400 mm.sup.2. It is significant to point out that just one
void of one micron diameter in a 1 mm.sup.2 area represents less
than 1 part per million.
[0101] In the case of fiber polymeric composites, if voids were to
occur in diameter sizes below the above visual count level, given
their relative size and dispersion with respect to known fiber
diameter of 2 to 13 microns, in the prior art, voids could still
affect fiber wet out by the resin, if they are very numerous and in
the form of very thin gas layers. Such voids would still
significantly interrupt interfacial boding, and thus, affect
mechanical properties. Notwithstanding, a method capable of
achieving void freeness could still be expected to generally
increase significantly the longitudinal and transverse elongation
moduli and associated strengths, and particularly transverse
strength properties.
[0102] Likewise, in the case of aggregate polymeric composites,
void-free polymer concrete composites made with the formulation of
one of the examples in the invention, do not exhibit
oscilloscopically discernible partial discharges in prototype
insulators when subjected to high voltages, at least below 90-100
KV, while only very modest partial discharges would be seen
starting above this range. Optimized aggregate and resin
formulations of dielectric polymer concrete composites, on the
other hand, can significantly increase the above-threshold of
partial discharge initiation and the overall dielectric strength of
void-free aggregate polymeric composites.
[0103] In conclusion, using this new understanding of voids and
their sources, a generic inventive method yielding a void-free and
occlusion free composite material was derived.
Application of the Generic Method to Fabrication Processes
[0104] The generic method of the invention for producing two
primary phase void-free/gas occlusion free unsolidified compounds
can be applied to specific present art fabrication processes. In
particular, the generic method can be most effective in the
manufacture of thermosetting polymeric compounds and composites
where the primary solid phase materials, (are either packed fibers
in fiber reinforced polymer composites or granular aggregates in
aggregate reinforced polymer composites). Such composites and
compounds generally exhibit low bulk densities indicating large
amounts of entrained air and other gases in the solids.
[0105] Tables 1 and 2, and the accompanying legend, further
illustrate how the generic method can be applied to produce two
primary phase, thermosetting polymeric compounds and composites,
combining the void free method with conventional mixing and forming
processes (batch mixing, continuous mixing or combinations of
both). As further shown in Tables 1 and 2, the void free method can
be used to fabricate a vast array of thermosetting polymeric
composites where the reinforcing solids in the primary solid phase
can be either fiber or aggregates, or a combination of both, and
where the primary liquid phase can be any thermosetting polymer
resin system and monomer, either extended or not with filler solid
materials intended to modify the properties of the binding resin
matrices.
[0106] A. Batch Mixing and Batch Forming Processes
[0107] As illustrated in table 1, the generic method can be used in
batch mixing and forming processes. Moreover, using the inventive
method, these batch fabrication processes can be used to produce an
array of void-free and gas occlusion free compounds and composites.
The choice of matrix reinforcement for the batch processes can be
selected from either the fiber or aggregate class of solids. The
legend, seen below, gives an explanation for each of the numbers
contained in Table 1.
1TABLE 1 BATCH MIXING AND BATCH FORMING PROCESSES PROCESS STAGES
& CHARACTERIZATIONS OF TYPICAL THERMOSETTING POLYMERIC
COMPOUNDS AND COMPOSITES WITHIN RANGE OF PATENT TWO PHASE BATCH
MIXING BATCH FORMING PROCESSES MIXER TO STORAGE TO MIXER MIXING
TYPE IN MOLD MIX MOLD TO MOLD MATRIX AND FORM AGGRE AGGRE
REINFORCEMENT FIBER FIBER GATE GATE STAGES GENERIC PRODUCTS FRP/RTM
BMC PC PC STAGE Washing primary 1.1. and 1.1. and 1.1. and 1.1. and
I Solid Phase with 1.2 1.2 1.2 1.2 Condensable Gas. (Primary Liquid
Phase degassed by conventional methods.) STAGE Air free Mixing of
two 2.2 2.5 2.1 2.1 II Primary Phases in presence of condensable
gas only STAGE Condensation of 3.3 3.2 3.1 and 3.1 III Condensable
Gas. 3.4 STAGE Uncured compound N/A 4.1 4.1 N/A IV storage STAGE
Composite final 5.1 5.1 and 5.1 and 5.1 V forming and curing 5.2
5.2
LEGEND TO TABLES 1 AND 2
Process Stages and Characterization of Typical Thermosetting
Polymeric Compounds and Composites Within Range of Patent
[0108] Stage 1
[0109] De-Airing of the Two Primary Phases Prior to Their
Mixing
[0110] Process 1.1
[0111] Replace air in solids by washing with a condensable gas
[0112] Process 1.2
[0113] Conventional thin film vacuum de-airing of liquid resin
system
[0114] Characterization at Stage 1
[0115] Voids inside solids are occupied only by condensable gas and
solid mass is soaked in a condensable gas medium. Liquid resin
system is air free.
[0116] Stage 2
[0117] Air-Free Mixing of the Primary Phases in Presence of
Condensable Gas Phase Only
[0118] Process 2.1
[0119] Mechanical agitation in mixing device
[0120] Process 2.2
[0121] Pressurized injection of liquid resin system into solids
[0122] Process 2.3
[0123] Combination of Process 2.1 and 2.2
[0124] Process 2.4
[0125] Continuous immersion of solids in liquid resin system
tank
[0126] Process 2.5
[0127] Mechanical kneading in mixing device
[0128] Process 2.6
[0129] Mechanical pressure kneading in SMC machine
[0130] Characterization at Stage 2
[0131] Unsolidified, two-primary phase mixed state compound having
dispersed occlusion bubbles of condensable gas only.
[0132] Stage 3
[0133] Condensation of Condensable Gas, Dispersion and Diffusion of
Condensed Gas
[0134] Process 3.1
[0135] Mechanical vibration under vacuum and condensable gas
[0136] Process 3.2
[0137] Mechanical pressure
[0138] Process 3.3
[0139] Hydraulic pressure on resin system
[0140] Process 3.4
[0141] Gas pressure
[0142] Characterization at Stage 3
[0143] Unsolidified two primary phase mixed state compound lacking
voids and gas occlusions.
[0144] Stage 4
[0145] Unsolidified Void-Free Compound Storage (If Applicable)
[0146] Process 4.1
[0147] Storage at below ambient temperature
[0148] Note: Storage conditions must maintain Stage 3
characterization.
[0149] Stage 5
[0150] Solid Composite Final Forming and Curing Under Absolute
Pressure at Least Equal to Vapor Pressure of Condensable Gas at
Specified Maximum Process Temperatures
[0151] Process 5.1
[0152] External pressure applied to composite in mold
[0153] Process 5.2
[0154] Mechanical pressure and heat of forming dies
[0155] Process 5.3
[0156] Process' own pressure
[0157] Final Characterization
[0158] Formed solid composite product free from air and gas
occlusions, voids.
[0159] B. Continuous Processes
[0160] As illustrated in Table 2, the generic method can be used in
continuous mixing processes. In this case, the forming protocol can
be either batch or continuous. Moreover, using the inventive
method, these continuous fabrication processes can be used to
produce an array of void-free and occlusion free compounds and
composites. The choice of matrix reinforcement for the batch
processes can be selected from either the fiber or aggregate class
of solids. The legend above gives an explanation for each of the
numbers contained in Table 2.
2TABLE 2 CONTINUOUS MIXING WITH BATCH AND CONTINUOUS FORMING
PROCESS STAGES & CHARACTERIZATIONS OF TYPICAL THERMOSETTING
POLYMERIC COMPOUNDS AND COMPOSITES WITHIN THE RANGE OF PATENT TWO
PHASE CONTINUOUS MIXING BATCH FORMING CONTINUOUS FORMING PROCESSES
MIXER TO MIXER IN LINE MIXING FORMING MIXING TYPE STORAGE TO TO
CONTINUOUS AGGRE MATRIX MOLD MOLD FIBER GATE REINFORCEMENT AGGRE
AGGRE PULTRU FILAMENT CENTRU GENERIC FIBER GATE GATE SION WIND
FUGAL STAGES PRODUCTS SMC/TMC PC PC FRP FRP PC STAGE Washing
primary 1.1. and 1.1. and 1.1. and 1.1. and 1.1. and 1.1. and I
Solid Phase with 1.2 1.2 1.2 1.2 1.2 1.2 Condensable Gas. (Primary
Liquid Phase degassed by conventional methods.) STAGE Air free
Mixing of two 2.6 2.3 2.3 2.4 2.4 2.3 II Primary Phases in presence
of condensable gas only STAGE Condensation of 2.6 3.2 3.2 5.3 5.1
5.3 III Condensable Gas. STAGE Uncured compound 4.1 4.1 N/A N/A N/A
N/A IV storage STAGE Composite final 5.2 5.1 and 5.1 5.3 5.3 5.3 V
forming and curing 5.2
[0161] In fabricating polymeric thermosetting composites by the
void free method, conventional pressure vessels adapted as needed,
are used to maintain a pressure-controlled, air-free environment.
Most preferably, a vacuum source should be used. In particular, in
the three stages of the generic method, the pressure vessel must be
connected to external pressure sources designed to operate at
process temperatures in a pressure range from about 1.2 to 3 times
the vapor pressure of the condensable gas selected. These pressures
will generally be sufficient to force the liquid phase to fill the
voids during stage III.
[0162] Application of the Generic Method to the Production of
Compounds and Composites
[0163] The generic process of the invention for two primary phase,
non-condensable gas occlusion free and void-free solidifiable
compounds can be applied specifically to various technologies
common in the field of polymeric composites. FIGS. 3-5 illustrate
how both thermosetting polymer concrete composites and fiber
reinforced thermosetting polymer composites can be produced from
the generic method of the present invention with two additional
successive processing stages that take the characterized
non-condensable gas occlusion free and void-free compound to final
void-free polymeric composite.
[0164] Detailed descriptions of preferred embodiments illustrating
the application of the generic inventive method to the production
of two-primary phase, void-free compounds and composites are shown
in FIGS. 3-5. These figures are illustrations of the inventive
generic method used to produce void-free polymeric composites by a
variety of methods known in the art. FIGS. 3 and 4 are examples of
void-free polymer concrete composites, and FIG. 5 is an example of
a void-free fiber reinforced polymer composite produced by Resin
Transfer Molding (RTM). Additionally, these figures show flow
charts of specific fabrication methods applied in each of the
successive three stages described in the inventive generic
production method, followed by up to two additional successive
stages required to yield the respective final void-free polymeric
composites. The generic method is likewise applicable to paints and
gel coats, which are used as barriers to protect the external
surfaces of reinforced polymer composites and polymer concrete. Gel
coats are polymeric compounds (solidifiable liquids) filled with
thixotropic solids (pyrogenic or fumed silicas, for example) and
are known in the industry to contain a significant amount of voids
due to entrained air. Because these large and numerous voids are
unsightly, gel coats are heavily pigmented to mask their
presence.
[0165] A. Polymer Concrete Composites, Methods and Materials
[0166] 1. Batch Polymer Concrete
[0167] Polymer concrete (PC) composite sample in FIG. 3 is made by
batch processes in four successive stages to yield a
non-condensable gas occlusion free and void-free solid polymer
concrete material. The description of these stages is as follows
per FIG. 3 and as specified in Table 3.
[0168] i. Stage I
[0169] Elimination of Air Water Vapor and Other Gases from the
Primary Solid Phase in Parallel with Degassing of the Primary
Solidifiable Polymer Liquid Phase
[0170] Using the present invention, the two primary phases are
generally processed prior to their mixing, with each phase being
degassed separately by a different method. These two degassed
phases are then brought together and mixed under air free
conditions. The key objectives in the method are: 1) to completely
eliminate air with associated water vapor and traces of any other
gases by displacing them, and, thereby, filling the voids of the
primary solid phase materials with a condensable gas prior to
mixing, and 2) in a separate process, to eliminate air and traces
of other gases from the liquid resin system by degassing the liquid
under high vacuum using conventional thin film methods prior to
mixing. The two air free phases can then be mixed under air free
conditions where the only gas present is the condensable gas used
to wash the solid materials.
[0171] Air and associated water vapor and other gases which fill or
are entrained in dry reinforcing materials, used in this batch
mixing example, are eliminated by placing the solids inside a
vessel connected to a vacuum source while using the apparatus
illustrated in FIG. 6. Condensable gas in the liquid state at
ambient temperature and atmospheric pressure is fed into the
inclined vessel. The amount of condensable gas in the liquid state
is dosed so that at least twice the void volume of the vessel and
void volume in the packed aggregates will be occupied by the
condensable gas upon its evaporation. Evaporation of the
condensable gas in the liquid state is initiated by applying a
vacuum to the closed vessel, preferably with the vessel and
contents at rest, and with a stream of condensable gas rising from
the bottom surface of the vessel upward through the packed solids
to the upper vacuum port. This vacuum is pulled until the entire
liquid content has evaporated and then the vacuum port is closed.
The chosen condensable gas will thus have completely displaced and
replaced the entrained air, water vapor, and other gases in the
voids of the solids and in the free volume of the vessel.
Optionally, the vessel can be heated externally in order to
maintain the initial system temperature to compensate for the heat
intake of the endothermic evaporation process of the condensable
gas and also to ensure the condensable gas remains in gaseous
state. The gas process conditions at the end of evaporation of the
condensable gas must be maintained so that external air is
prevented from contaminating the contents of solids soaked with
condensable gas in gaseous state, and more importantly, to prevent
reversion of the condensable gas replacement in the solids by
external air. The degassified solidified liquid resin phase is then
fed into the closed vessel to begin batch mixing with the solids
soaked with condensable gas.
[0172] Air, water vapor, and other gases dispersed in the liquid
thermosetting resin system are likewise also eliminated prior to
mixing in a separate process by using any conventional, effective,
thin film vacuum degassing process. As previously stated, the resin
system is a second source of potentially large volumes of air and
other gases that would be incorporated into the two primary phase
mixed compound if, as in prior art, no step is performed to ensure
their complete removal.
[0173] ii. Stage II
[0174] Air Free Mixing of the Two Air Free Primary Phases
[0175] The two air-free phases are then mixed under air free
conditions in the closed mixer at process temperature and a
suitable condensable gas vaporization pressure. Here the only gas
present is the condensable gas used previously to wash the solid
materials. Moreover, mixing occurs in an atmosphere of the
condensable gas. Thus, in the inventive process the mixing process
of the two primary phases takes place in a medium where the third
phase, i.e., the gas phase has been rendered free of air by
condensable gas replacement per the invention.
[0176] When mixing is complete, the condition of the mixed state
compound will be otherwise identical to that in prior art
processes, except that in the invention the third phase consists of
a condensable gas phase, instead of air, water vapor and other
gases. Furthermore, the condensable gas is randomly dispersed
throughout the viscous liquid phase by the mixing of the phases. At
this point, the gas phase is in the form of discrete spheres or
bubbles suspended in the liquid phase or entrapped in the
interstices within the primary solid phase.
[0177] In this example of batch mixing and forming, the two primary
phase polymeric compound, as shown in FIG. 6, is poured into the
mold section of the vessel maintaining the mixing process
conditions. To accomplish this, as illustrated in FIG. 6, the mold
is attached to, and forming part of, the mixing chamber in the
vessel, and by pivoting the assembly, the contents in the mixing
chamber are gravity fed into the mold cavity. The accommodation of
the two phase mixed compound in the mold is completed by mechanical
vibration to pack the two phase mixed compound tightly to the shape
of the mold, thus ensuring all corners are filled, and at the same
time, dispersing the condensed gas droplets into the solidifiable
liquid system.
[0178] iii. Stage III
[0179] Condensation of the Condensable Gas
[0180] With the two phase compound in the mixed state sufficiently
packed into the mold, as shown above, the process pressure is made
at least equal to, or preferably higher than the condensable gas
vapor pressure at the process temperature. This enables the
absolute pressure at any point within the mixed state compound mass
to be at, or above, the condensable gas vapor pressure, thus
ensuring all dispersed condensable gas bubbles will condense, and
all voids thereby, will be filled with liquid resin. Under these
conditions, the condensable gas phase is totally condensed.
Sufficient time is allowed for the condensed gas in the liquid
state to fill voids throughout the mixed state compound, yielding a
void-free polymer concrete compound.
[0181] iv. Stage IV
[0182] Void-Free Compound Solidification to Form a Final Solid
Void-Free Polymer Concrete Composite Shaped by the Mold
[0183] The void-free polymeric concrete compound is allowed to
solidify in the mold. Upon complete cure, the void-free solid
polymer concrete composite part is removed from the mold.
[0184] As detailed in Table 3 below, this polymer concrete example
has been produced according to the four stage method described
herein. The particular formulation of the phases, choice of the
condensable gas, and process parameters were adjusted to produce a
void-free dielectric class polymer concrete composite meeting the
visual count void-free criteria and the electrical partial
discharge criteria indicated in the invention herein, and
illustrated in FIG. 8. Moreover, under these conditions, the final
composite is also a readily machineable material suitable for mass
production of a high voltage electric current insulator, as
illustrated in FIG. 8.
EXAMPLE 1
[0185] Table 3 reveals the material specification and process
parameters used to yield a void-free and occlusion free polymer
concrete material. The specific application of the generic method
used to produce the example material given in Table 3 is
illustrated in FIG. 3.
3TABLE 3 TWO PRIMARY PHASE BATCH MIXING, BATCH MOLDING, MIXER TO
MOLD METHOD POLYMER CONCRETE COMPOSITE Cast Dielectric Polymer
Concrete A MATERIAL SPECIFICATIONS (8-23) SOLID REINFORCEMENT
Aggregates, Silica, @ Bulk density 1.6 gr/ [gr] 3474.0 cc, @
Specific density 2.5 gr/cc, Max. Min. Diam. Diam. [mm] [mm] 0.595
0.420 22.40% [gr] 778.2 0.420 0.297 20.20% [gr] 701.7 0.297 0.149
35.50% [gr] 1233.3 0.149 0.000 21.90% [gr] 760.8 ATH BACO S5 [gr]
1362.0 Total Solids 4836.0 CONDENSABLE GAS Methyl-Methacrilate, MMA
[gr] 48.4 LIQUID RESIN MATRIX Thermoset Resin Palatal A 430, [gr]
987 bisphenol A polyester resin Mono Styrene [gr] 177 Resin Matrix
Viscosity, Ford # [sec] 34 4 ASTM cup @ 25.degree. C. Catalyzation
System (Inmediate use) Cobalt Octoate 6%, [% resin base] 0.10% DMA,
N,N-dimethylaniline, [% resin base] 0.15% MEKP, Methyl Ethyl
Ketone, [% resin base] 1.00% Peroxide, B PROCESS PARAMETERS STAGE
I, WASHING PRIMARY SOLID PHASE Wetting Solid phase with liquid MMA
Closed mixer can, [rpm] 40 Absolute pressure, [Hg mm] 760 System
temperature, [.degree. C.] 30 Time, [minutes] 10 Gas vaporization,
washing and air replacement with gas MMA Closed mixer can, [rpm] 0
Absolute pressure, [Hg mm] 50 Initial Temperature, [.degree. C.] 30
Time, [minutes] 15 STAGE II, AIR FREE MIXING OF TWO PRIMARY PHASES
Mixing Process Resin Injection This process requires previous
deaired liquid phase Absolute pressure, [Hg mm] 760 Closed mixer
can, [rpm] 0 Temperature, [.degree. C.] 25 Time, [minutes] 5 Mixing
in presence of condensable gas Closed mixer can, [rpm] 40 Absolute
pressure, [Hg mm] .gtoreq.50 Temperature, [.degree. C.] 30 Time,
[minutes] 5 Mold Filling Process Mold attached to mixer Absolute
pressure, [Hg mm] .gtoreq.50 Temperature, [.degree. C.] 30 Time,
[minutes] 1 STAGE III, CONDENSATION OF CONDENSABLE GAS Absolute
pressure, [bar] 10 Time, [minutes] Included in Stage IV STAGE IV,
COMPOSITE FINAL FORMING & CURING Curing Absolute pressure,
[bar] 10 Temperature, [.degree. C.] Room temperature Condensation,
Forming, Curing [minutes] 60 and Demolding Time,
[0186] 2. Continuous Mixing Polymer Concrete
[0187] FIG. 4 illustrates a continuous mixing process in five
successive stage to yield a void-free polymer concrete composite
material, including an optional storage stage between the
characterized two phase non-condensable gas occlusion free and
void-free polymer concrete compound and the final solid void-free
polymer concrete composite. The description of these stages is as
follows, as shown in FIG. 4.
[0188] i. Stage I
[0189] Elimination of Air and Other Gases From the Primary Solid
Phase in Parallel with Degassing of the Primary Solidifiable
Polymer Liquid Phase
[0190] The two primary phases are generally processed as in Stage I
above. However, as this embodiment is produced in a continuous
process, there are differences in the condensable gas washing
method.
[0191] In continuous mixing apparatus embodiments for polymer
concrete, illustrated in FIG. 7, the solids with entrained air,
water vapor, or other gases are first gravity fed continuously
under ambient conditions into a closed vertical solid loading
hopper, and through a rotary seal valve located on the top of the
hopper that prevents external air from entering and breaking
vacuum. Vacuum in the loading hopper reduces the volume of
entrained air and other gases in the solids and prepares the
primary solid phase for gravity discharge through a lower seal
valve into a vertical condensable gas replacement column, which is
also under vacuum. The gas replacement column has a lower discharge
through the shroud into the internal screw chamber of a
conventional, continuous screw type, two primary phase solid/liquid
mixing machine. Condensable gas, which is evaporated externally and
fed through valves in the shroud of the continuous mixing machine
first soaks the solids inside the screw chamber, and then streams
upward towards the upper zone of the gas replacer column, soaking,
in counter-current, the downward traveling solids of the primary
solid phase. Continuous feed of de-aired solids for mixing is
produced by the rotation of the mixing screw which advances the
de-aired solids forward, where they are soaked in condensable gas,
and allowing continuous gravity feed of processed solids from the
filled gas replacement column.
[0192] The primary liquid polymeric resin phase is degassed free
from air and other gases in a separate process using any
conventional, effective, thin film degassing process.
[0193] ii. Stage II and Stage III
[0194] Air Free Mixing of the Two Primary Phases, and Subsequent
Condensation
[0195] Air free continuous mixing process in the screw type machine
is accomplished by screw rotation which advances forward the
primary phase solids soaked in condensable gas and by feeding the
degassed solidifiable liquid phase into the screw shroud. Mixing is
followed by pressurized condensation of the condensable gas and
densification of the mixed state compound in the screw type mixing
machine. These steps are represented by successive adjacent zones,
as illustrated in FIG. 7. The two phase void-free unsolidified
compound characterized in the generic method of invention is
discharged from the continuous mixing machine through a collapsible
rubber spout choked by adjustable springs set to close down when
the machine looses process speed, or to shut when stopped. The
spout allows essential air-free continuous discharge as it prevents
atmosphere air from penetrating inside the screw and shroud of the
machine discharge port. The rubber spout is sized to suit the
machine speed or capacity, compound characteristics, and other
process parameters.
[0196] iii. Stage IV
[0197] Void-Free Compound Packaging for Storage
[0198] Void-free compound packaging for storage is done using
collapsed, air free, flexible material packaging containers of
desired shape and dimension, which are attached onto the discharge
spout of the continuous mixing machine to successively receive the
void-free solidifiable polymer concrete compound. Pressure exerted
by the rotation of the mixing screw will force the compound out of
the discharge port of the machine into the collapsible rubber
spring loaded spout, which is forced to remain open by the moving
void-free material pressing against the set pressure of the closing
springs. In this way, the compound is loaded into the collapsed
flexible container attached to the spout. As an individual
container is filled, a proximity signal mechanism increases the
closing spring tension, collapsing the rubber spout shut while the
mixing machine continues to run. At this point, the volume of
compound discharged expands the rubber body of the shut spout,
which now acts as a compound accumulator, increasing its original
volume. Meanwhile, the compound filled container is externally
detached from the rubber spout and a new empty collapsed, air free,
flexible container is re-attached on the spout to begin a new
cycle. The high tension level of the springs is then signaled to
start releasing back to the normal setting. The accumulated volume
of void-free compound in the rubber spout thus begins to force
itself out of the spout and into the new empty collapsed flexible
container, as the spout spring tension becomes released to allow
material discharge.
[0199] If used as forming molds, the containers filled with
void-free unsolidified compound are sealed and the placed into a
conventional autoclave, to harden in the shape of the containers at
adequate combinations of pressure, temperature and time.
Alternatively, the flexible container with unsolidified compound
can be subsequently shaped by placing the sealed container and
contents into a two or more part sectional mold, in which, by a
combination of pressure and temperature the void-free unsolidified
compound will harden into a solid, void-free, shaped polymer
concrete composite.
[0200] Alternatively, if desired the filled flexible containers are
sealed and placed in storage at reduced temperature, preferably in
the range of +20.degree. C. to -20.degree. C., for up to 6 months
depending on the characteristics of the solidification substances
incorporated in the liquid resin system.
[0201] B. Fiber Reinforced Polymeric Composites, Methods and
Materials
[0202] FIG. 5 illustrates a batch mix and forming processing by the
inventive method in four successive stages to yield a void-free,
solid, fiber reinforced polymer composite material in laminar
shape, formed by Resin Transfer Method (RTM). The description of
the RTM process stages are as follows, as per FIG. 5 and Table
4:
[0203] i. Stage I
[0204] Elimination of Air and Other Gases From the Primary Solid
Phase in Parallel with Degassing of the Primary Solidifiable
Polymer Liquid Phase
[0205] For RTM, and similarly for the newer SCRIMP process, vacuum
is applied in the fiberglass solids in the mold before mixing with
the resin. In the generic method, the fiber is first washed with a
stream of condensable gas through the same resin injection ports
(particularly in SCRIMP), and the condensable gas is injected or
infused while the system is still under vacuum. The process is
continued until condensable gas is detected at the vacuum exhaust
ports. Under these conditions the condensable gas stream will have
adequately replaced all entrained air, traces of water vapor in the
fibers, and other gases that may have been entrained by the solids.
However, in the case of complex shape parts, or where mold corners
are remote or difficult to access by the condensable gas stream,
the gas replacement may not be totally effective. For this case,
the generic process offers an additional alternative which consists
of cutting the vacuum flow, but retaining vacuum presence in the
system. This step is followed by pressure injected, outside
evaporated, condensable gas at an elevated temperature, above the
system's temperature, generally in a range of up to +40.degree. C.
above ambient temperature. This gas injection is continued until
the gas pressure in the outside evaporator, at the constant above
ambient temperature selected, is in equilibrium with the internal
pressure of the system. This step is maintained until the amount of
liquid in the external gas evaporation chamber has been evaporated.
The additional external condensable gas at higher temperature that
has been introduced will thereby elevate the temperature of the
fiber solids and, thus, is able to reach the mold corners and other
difficult spots because of its higher pressure. In this manner, the
condensable gas is able to disperse some of the original entrained
air, water vapor and other non-condensable gases that may not have
been totally removed. As the temperature of the condensable gas
drops by giving off its heat to the colder solids, it will
partially condense until pressures are in equilibrium. At this
stage vacuum is reestablished in the system and the condensable gas
that has condensed will re-evaporate at each condensation spot and
stream out under the vacuum, entraining the remaining air, water
vapor and other gases. The solids are now air-free, water
vapor-free and soaked with condensable gas.
[0206] The reinforcing solid, in Example 2, is a laminar fiberglass
mat which is placed inside a close mold. The same mold will serve,
in this case, as a degassing device, mixing device, condensation
device and solidification/molding device. Upon placement of the
fiberglass mat, the mold is closed and evacuated while a
condensable gas, preferably evaporated externally from a gasifiable
liquid, is fed into the closed mold under vacuum for a sufficient
time to completely soak the fiber glass mat and to displace all
entrained air and other gases in the fiber glass solid. O.sub.2
presence in the exhaust ports of the mold can be monitored with an
O.sub.2, sensor. The processed primary fiber glass phase is now
air-free, soaked with condensable gas, and ready for mixing with a
separately degassed primary liquid polymer resin phase. Liquid
phase degassing is done by conventional thin film technology as
disclosed in prior art.
[0207] ii. Stage II
[0208] Air Free Mixing of the Two Air Free Primary Phases
[0209] Stage II, air-free, two-primary phase mixing begins by
infusing (SCRIMP) or injecting (RTM) the degassed primary liquid
resin system under vacuum in the system. It is particularly
important that the resin system is degassed and air-free. Once the
liquid resin has been introduced filling the mold and soaking the
solid phase, condensable gas in the system will be occluded in the
mix.
[0210] Liquid polymer resin is injected under positive pressure per
conventional RTM technology through conveniently located ports and
distribution channels into the mold, until the liquid resin emerges
from the separate vacuum exhaust ports. At this point both the
vacuum and resin ports are closed and left closed until the
beginning of the condensable gas condensation.
[0211] iii. Stage III
[0212] Condensation of the Condensable Gas
[0213] Depending on the choice of condensable gas, condensation of
the condensable gas, typically Stage III may have already occurred
in Stage II, under the pressure of the resin injection. This is
more likely in cases such as the straight forward laminar shape of
the mold used in Example 2, and detailed in Table 4. However, in
more complex shapes, and/or pieces with variable sections, it is
preferred to place the closed mold with contents in a pressure
chamber and pressurize the system to an adequate pressure for a
sufficient time to achieve a void-free fiber reinforced polymer
compound of the quality level required per conventional RTM
technology. The characterized compound invention condition will
have been reached when:
[0214] 1) Washing of air, water vapor and other gases by the
condensable gas has been accomplished; here entrained water vapor
is deleterious and eliminating it improves the polymerization
reaction.
[0215] 2) Soaking of the fiber surfaces with condensable gas
modifies and lowers the glass fiber surface tension level; the
liquid when coming in contact with the fiber to form the
interfacial bond now comes in contact first with the condensable
gas soaked fiber surfaces; and, moreover, without back pressures
from non-condensable gas occlusions; wet out of the fiber by the
resin and interfacial bonding will be improved.
[0216] iv. Stage IV
[0217] Solidification of the Void-Free Fiber Reinforced Polymeric
Compound into a Void-Free Composite Shaped by the Mold
[0218] Solidification of the compound will occur, according to the
polymerization art described in RTM technology, to produce a final
solid, laminar shaped, void-free fiber reinforced polymer composite
that complies with the visual count void-free criteria established
in the invention. A detailed data sheet is given in Example 2
below.
EXAMPLE 2
[0219] Table 4 reveals the material specifications and process
parameters to yield a void-free and occlusion free fiber reinforced
polymer (FRP) material. The specific application of the generic
method used to produce the example material given in Table 4 is
shown in FIG. 5.
4TABLE 4 TWO PRIMARY PHASE BATCH MOLDING, IN MOLD MIX AND FORM BY
RTM METHOD LAMINAR FRP COMPOSITE Laminar F.R.P. R.T.M. (FV-9) A
MATERIAL SPECIFICATIONS SOLID REINFORCEMEl Filament Fiber, Glass
fiber (MAT 450 gr/m2) [gr] 121 CONDENSABLE GAS Methyl-Methacrilate,
MMA [ml] 6 LIQUID RESIN MATRIX Thermoset Resin Palatal P 80,
Unsaturated poly- [gr] 314.5 ester, Viscosity, Ford # 4 ASTM [sec]
34 cup @ 25.sup.t Catalyzation System (Inmediate use) Cobalt
Octoate 6%, [% resin base] 0.10% DMA N,N-dimethylaniline, [% resin
base] 0.15% Methyl Ethyl Ketone, Peroxide, [% resin base] 1.00% B
PROCESS PARAMETERS STAGE I, WASHING N/A PRIMARY SOLID PHASE Gas
replacement RTM mold Absolute pressure, [Hg mm] 40 Temperature,
[.degree. C.] 30 Time, [minutes] 12 STAGE II, AIR FREE MIXING OF
TWO PRIMARY PHASES Mixing Process Resin injection This process
requires previous deaired liquid phase Absolute pressure, [Hg mm]
760 Temperature, [.degree. C.] 25 Time, [minutes] 3 Fiber Glass in
RTM mold RTM mold filled with fiber glass and inunded condensable
gas Absolute pressure, [Hg mm] .gtoreq.50 Temperature, [.degree.
C.] 25 STAGE III, CONDENSATION OF CONDENSABLE GAS Absolute
pressure, [bar] 6 Time, [minutes] Included in Stage IV STAGE IV,
COMPOSITE FINAL FORMING & CURING Curing Absolute pressure,
[bar] 6 Initial temperature, [.degree. C.] Room temperature Time,
[minutes] 35 Condensation, Forming, Curing 90 and Demolding
Time,
[0220] C. Conclusion
[0221] The descriptions detailed above illustrate the many facets
and applications of the generic void-free method in composite
technology and production. The inventive method can be utilized to
produce a vast array of void-free polymeric compounds and
composites. Moreover, a polymer concrete sample and a fiber
reinforced polymer composite sample free of gas occlusions and
voids has been produced and detailed herein.
[0222] Apparatus
[0223] a. Apparatus for Batch Production of Void-Free Polymer
Concrete Compound and Composites
[0224] FIG. 6 illustrates a preferred embodiment of the apparatus
for batch replacement of air, water vapor, or other gases normally
contained within the interstices, spaces or voids of the primary
solid phase at ambient temperature and pressure, by a condensable
gas prior to batch mixing with a solidifiable liquid phase to
yield, a two-primary phase solidifiable polymer concrete compound
free from non-condensable gas occlusions. The compound is poured
from the mixer into a mold in air-free and non-condensable gas free
environment. When the solidifiable compound is in the mold, the
apparatus is pressurized to condense the condensable gas in the
compound already in the mold, and optionally, can be solidified in
the mold to produce a gas occlusion free and void-free composite
formed in the shape or configuration of the mold. The apparatus 30
shown in FIGS. 6A and 6B include mixing chamber 31 with a mold 32
attached to it. The apparatus 30 has 2 operating positions: for
mixing (FIG. 6a) and for pouring the solidifiable mixed compound
into the mold (FIG. 6b). The primary solid phase is placed in the
mixing chamber 31, preferably with a Class I gasifiable liquid.
Vacuum is applied through the vacuum inlet port 33 and the entire
assembly is rotated mechanically about its longitudinal axis as
indicated at 34 for 1 to 2 minutes with vacuum shut off. The
contents of solids and gasifiable liquid are washed thoroughly
together. This allows the gasifiable liquid to completely wet out
the solids and to begin an evaporation process. The resulting
condensable gases evaporated from the liquid to replace the air,
water vapor associated with air, or other gases in the solids. The
system is stopped for 1 or 2 minutes and vacuum reestablished to
evacuate the air, water vapor associated with air or other gases
entrained in the condensable gas. The wash cycle is repeated,
preferably at least four times, without addition of condensable
gas. Upon completion of the washing stage, the primary solid phase
will have all its voids filled with condensable gas.
[0225] At this point the primary solidifiable liquid resin system
previously degassed is infused by vacuum into the apparatus through
the inlet port shown in FIG. 6a. A mixing cycle of the two primary
phases in the presence of condensable gas only is started by
mechanical rotation of the apparatus, with vacuum shut off, and
continued for 4 to 5 minutes. At the end of the mixing cycle the
two primary phase solidifiable mixed compound is free from
non-condensable gas occlusions and ready to be poured and gravity
fed into the attached mold 32.
[0226] As illustrated in FIG. 6b, this step is accomplished by
rotation of the apparatus 30 until the attached mold 32 is in the
bottom position. Once the solidifiable mixed state compound is
lodged in the mold, at rest, a thin film of liquid resin is formed
over the top exposed surface after a short period of vibration
(depending on the size and shape of the mold of) 1 or more minutes
with the vibration device 39. Pressure in the apparatus 30 is
increased by allowing pure CO.sub.2 gas to enter into the apparatus
through inlet port 35. This pressurizing gas is at atmospheric
pressure or preferably at an absolute pressure at least equal to 2
times the condensable gas vapor pressure at the process
temperature. The CO.sub.2 gas environment maintains the system air
free and eliminates presence of O.sub.2 from outside air to ensure
optimal solidification of the primary solidifiable liquid phase in
the compound. Upon pressurization, the pressure of the CO.sub.2 is
exerted on the mold contents through the thin barrier layer of
resin on its upper exposed surface, which is sufficient to prevent
CO.sub.2 gas dispersion into the material in the mold, yet its
pressure will condense the condensable gas within the solidifiable
mixed state compound in the mold, and further maintenance of
CO.sub.2 gas pressurized condition for at least 1 minute will
ensure the solidifiable liquid phase will enter all voids in the
compound. At this stage, the two primary phase solidifiable
compound in mixed state in the mold 32 will have reached the
characterized condition of freedom from non-condensable gas
occlusions and voids. To obtain a void-free molded composite, the
mixed state compound is left to solidify in the mold 32 under
positive CO.sub.2 absolute pressure conditions. If desired,
consolidation of the solidifiable compound in the mold can be
facilitated by the use of a vibration device 39 mounted on the mold
32, prior to curing.
[0227] It will also be noted that, in the apparatus 30, the mold 32
is removable as indicated by the bolted joint 36 and bolt fasteners
37. This allows the compound to be cured in the mold 32 off-line
while a new, empty mold is reattached to the apparatus 30 so that
compound production can be expedited. Likewise, the mixer 31 is
demountable at a similar bolted joint 38 to allow maintenance and
repair, and also to allow attachment of other mixing chambers 31 of
differing capacities and geometrical shapes, or allow attachment of
a hopper equipped with a conventional air tight auger screw type
discharge device in place of mold 32, to intermittently discharge
discrete metered amounts of gas occlusion free solidifiable
compound from the apparatus into external molds.
[0228] b. Apparatus for Continuous Void-Free Polymer Concrete
Compound Production
[0229] FIG. 7 illustrates a preferred embodiment of an apparatus 40
for continuous void-free production of polymer concrete. As
explained above in detail, the apparatus 40 can be used in a method
of production involving the replacement of air, water vapor or
other gases normally contained within the interstices, spaces or
voids of the primary solid phase at ambient temperature and
pressure, by a condensable gas prior to continuously mixing with a
solidifiable polymer concrete compound free from non-condensable
gas occlusion and voids.
[0230] The apparatus 40 includes a condensable gas
displacement/replacemen- t counter-current column 46 with an upper
zone vacuum chamber 26. Within the chamber 26, a controlled vacuum
condition is maintained to exhaust air, vapors and gases, normally
entrained in the primary solid phase which are continuously
displaced/replaced by a stream of condensable gas. A lower
discharge zone 27 is connected at one end to the column 46 and to
the shroud 49 of a continuous screw type mixing apparatus 28.
Inlets 48 for the condensable gas are provided in the shroud 49 to
flood with the condensable gas the discharge zone 27 of the column
46 and the adjacent volume inside the shroud where processed solids
are discharged. Condensable gas horizontal deflector baffles 47 are
provided inside the column wall to effectively distribute the
upward stream of condensable gas, traveling towards the upper zone
vacuum chamber 26, with the primary solid phase falling by gravity
in the column. This counter flow of condensable gas produces a
washing effect which displaces and replaces entrained air and other
gaseous substances in the primary solid phase by the condensable
gas.
[0231] Since the counter flow of condensable gas is at positive
pressure flow to facilitate the washing process, it will be
recognized that this streaming condition reduces consumption of the
condensable gas and increases the efficiency of the apparatus 40.
Oxygen sensing devices 62 are provided in the column 46 at
different levels to monitor the presence of air and to ensure no
oxygen is detectable in the lower discharge zone 27 or in the
flooded shroud zone 49 of the continuous mixing apparatus 40. This
monitoring is achieved by means of a gas control and feedback
system 30. If oxygen is detected by the monitors 62, the control
system 30 appropriately adjusts the level of condensable gas
entering the inlets 48. Optionally, in a preferred embodiment, a
vibrating device 60 with vibration control mechanism is attached
externally to the column wall to avoid agglomeration and promote
free flow of the primary solid phase, and also to ensure its
continuous gravity downward travel.
[0232] Flexible connections 63 are provided at the upper and lower
extremes of the column 46, to connect the column with the upper
zone vacuum chamber 26, and to connect the lower discharge zone 27
with the shroud 49. Structure is provided above the upper zone 46
of the column for a vacuum chamber 44 with an exhaust and a
receiving hopper 43, also under vacuum, for controlled feeding of
the primary solid phase into the column 46. The receiving hopper 43
is provided with rotating seal valves 42 and 45 located at its
upper inlet port 41 and at its lower discharge port to provide
passage, under vacuum, of the primary solid phase from atmospheric
conditions into the controlled vacuum gas displacer column 46. The
upper inlet port seal valve 42 of the hopper 43 is connected to the
external supply of primary solid phase at open atmospheric
conditions and prevents breaking vacuum inside the receiving hopper
43. The vacuum chamber 44 in the hopper 43 is provided with vacuum
to also assist in the reduction of the amounts of entrained gases
and vapors in the incoming primary solid phase as it continuously
passes through the hopper 43, so upon its discharge into the upper
zone 26 of the gas displacer/replacer column apparatus, the
entrained air, gas and vapor substances in the solids have been
significantly reduced by vacuum. The lower discharge seal valve 45
of the receiving hopper 43 allows the maintenance of differential
vacuum levels between the hopper 43 and the column 46 for more
effective control of the displacement/replacement function in the
gas replacer column apparatus. At the lower discharge 27 of the
column 46 into the continuous mixing device 49, the processed
primary solid phase is air and water vapor free and flooded with
condensable gas, essentially ready to begin the continuous mixing
process with a primary solidifiable liquid phase (which has been
previously degassed externally), to form a two primary phase
unsolidified polymer concrete compound exempt of gas occlusions,
and voids, as per the present invention.
[0233] The mixing apparatus 40 of the present invention is also
provided with a motor control 68 for controlling the operation of
the rotating seal valves 42,45. Sensors 69,70 located in the hopper
43 sense the level of the solids therein and provide a signal to
the controller 68. A control signal is then provided from the
controller 68 to the DC motor 72 controlling the operation of the
upper rotating valve 42. Likewise, sensors 64 and 65 located in
column 16 sense the level of the solids therein and provide a
signal to the controller 68. A control signal is then provided to
DC motor 67 for controlling the operation of the lower rotating
seal valve 45. Meters 66, 71 are provided in column 46 and the
hopper 43, respectively, in order to sense the vacuum level within
these enclosed containers.
[0234] The continuous mixing apparatus 40 comprises preferably a
continuous mixing device 27 of the shrouded rotating screw type,
appropriately modified to comply with the following
requirements:
[0235] 1. Condensable gas inlet ports 48 into the screw shroud 49
must be provided with a mechanism 30 for adjusting the pressure and
flow of the condensable gas. Inlet ports 48 should be suitably
located adjacent to the column discharge zone 27 where the air-free
primary solid phase, soaked with condensable gas, enters the screw
shroud 49, so as to provide a continuous counter-current stream of
condensable gas through the connection between the shroud and the
discharge zone moving upwards into the gas replacer column 46.
[0236] 2. The internal zone within the screw shroud 49 must be
maintained continuously flooded with condensable gas at all times
when the mixer 28 is running. Furthermore, that zone must be
provided with a shielding, such as a double seal device 55 to
maintain the drive extension 31 of the mixing screw 28 flooded with
condensable gas in liquid state to prevent contamination from leaks
of external atmospheric air. Furthermore, the drive extension 31
connects a reducer 59 mounted on the drive output of DC motor 58
which rotates the mixing screw 28. The level of liquid state
condensable gas in the double seal chamber 55 can be determined by
the gas level device 57.
[0237] 3. The entry port 50 for feeding degassed, air-free primary
solidifiable liquid phase into the continuous mixing device 40 must
be suitably located downstream, and sufficiently away from the
processed primary solid phase entry zone 32 of the shroud 49.
[0238] 4. The downstream configuration of the mixing screw 28 and
shroud 49 in the continuous mixing device between the solidifiable
liquid phase enter zone 33 and the final discharge port 53 of the
continuous mixing device is subject to the following design
requirements:
[0239] i) The rotating screw 28 must impart sufficient absolute
pressure within any point of the two primary phase mixed state
compound being formed as it advances towards the discharge port 53
and to completely condense the condensable gas within the primary
liquid phase of the mix and to force liquid resin into any voids.
Such pressure must be maintained over the range of screw
operational speeds, including its minimum speed. This may be
accomplished by means of an enlarged diameter section 54 of the
multisection mixing screw 28. This section 54 serves to increase
the pressure of the mixture within this condensation zone 34 by
reducing the annular space between the screw 28 and the shroud
49.
[0240] ii) The liquid state condensed gas must be sufficiently
dispersed and diffused within the solidifiable liquid phase of the
mix in the condensation zone 34, before the compound mix reaches
the discharge port 53 of the mixing device 40.
[0241] iii) Atmospheric air must be prevented from entering the
compound mix through the discharge port 53 and contaminating the
gas occlusion and void free two primary phase mixed unsolidified
compound.
[0242] 5. Machine void-free compound discharge must provide means
for discharge of a non-condensable gas occlusion free and void-free
compound so that its characterization is assured when the machine
stops, such as an air tight, sealable, flexible spout 73 to seal
off the external air entrance. Also provided is a means for
discharging the compound so that its void-free characterization is
assured, such as air tight, sealable, flexible spout stops 35 as
having spring or other biasing means to maintain tight closure. The
apparatus is further capable of accumulating discrete and
sufficient amounts of void-free polymer concrete compound in it to
enable intermittent discharge of the void-free material into
discrete receiving containers of discrete unit volume, under air
free conditions.
[0243] Thus, it will be appreciated that the principles of the
apparatus of the present invention can be applied to numerous other
continuous mixing devices having similar features.
Product and Applications
[0244] Electric insulators intended for high voltage applications
previously have been preferably made of porcelain materials.
However, more recently it bas been found that polymer concrete
could be used as the material for such insulator applications.
Additionally, these insulators provide advantages in both cost and
performance. U.S. Pat. No. 4,210,774, for example, discloses a
polymer concrete insulator having dielectric and mechanical
properties far superior to those of conventional porcelain
insulators.
[0245] However, an inherent disadvantage of polymer concrete
electric insulators has been the presence of voids or gas
occlusions, as the result of insufficient or inadequate degassing
and mixing of the solidified material. It is well known that
increased number of voids, or gas occlusion porosity, resulting
from air and associated water vapor entrainment in solids,
adversely affects the dielectric and mechanical strength of
insulators, and encourages partial discharges leading to early
failure within the material body. To overcome this problem,
ideally, a void-free material would be desirable for use in high
voltage electrical insulators.
[0246] The insulators prepared from special formulations for
void-free dielectric polymer concrete, as detailed in Example 1,
produced by the generic void-free method of the present invention,
are designed to be formed or shaped by machining the insulator
shape directly from cast void-free polymer concrete cylindrical
stock, or by conventional shape molding methods. The resulting
insulators formed by machining have controllable surface finish and
very tight dimensional tolerances, as well as excellent and
improved dielectric characteristics and mechanical strength. The
finish of the machined surfaces can be controlled for enhanced
adhesion of specialized material coatings in thin films on to the
machined surfaces, rendering the insulator non-hygroscopic and
hydrophobic for outdoor service.
[0247] Moreover, insulators fabricated from void-free dielectric
polymer concrete made in accordance with the present invention
exhibit dramatically increased voltage threshold for initiation of
partial discharges within the body of the insulator, thus extending
their useful life.
[0248] FIGS. 8A-8C illustrate an insulator produced from methods
and materials of the present invention. FIGS. 8A and 8C are top and
bottom views, respectively, and FIG. 8B is a longitudinal
cross-sectional view. The insulator 80 in FIG. 8 is a resistive
voltage grading device whose body 81, shields 84, all bores 83 and
holes 85 to install threaded metallic contacts 82, have been
machined from a cylindrical stock of void-free polymer concrete
composite material complying with both the visual count void-free
criteria of no visible voids of 0.5 micron diameter at 1250.times.
magnification and dielectric criteria of no visible partial
discharges seen in an oscilloscope screen when subjected to
voltages of 90-100 KV.
[0249] The good machinability of the void-free dielectric polymer
concrete material of the present invention enables production of
all classes and types of electric transmission and distribution
insulators, as well as other devices such as bushings and insulator
plates or rings. Insulators include suspension pin type, strain,
line post, etc., preferably in higher voltages ranges up to 100 KV
or even beyond. One important discovery from the work done in this
invention is that material formulations appropriate for void-free,
dielectric polymer concretes have also excellent machinability.
Another discovery is that finished electric insulators of high
quality can be efficiently shaped by conventional machining with
special cutting tools from cast polymer concrete stock material
produced using the inventive void-free method. Yet another discover
is that machining is a high efficiency and high productivity
forming method far superior to the conventional method of forming
insulators by shape molding materials in conventional shape molds,
in that better quality insulators can be produced faster, with
shorter lead times and at much reduced mold and labor costs.
Likewise, very accurately dimensioned dielectric polymer concrete
flat plates parts can be produced, cut from cast polymer concrete
stock into slabs and then surface finished by milling, drilling,
boring, etc. as required.
[0250] Methods & Apparatus for Large Scale Production of
Void-Free PC Composites
[0251] A. Overview
[0252] FIG. 9 illustrates the application of the present invention
to large scale manufacturing of void-free, and gas occlusion-free
PC composites. The embodiment includes provisions for in-process
quality control and for recycling non-conforming parts. The method
and apparatus disclosed in FIG. 9 represent an integrated and
rational sequence of linked unit processes that constitute a
complete industrial production line. The production line disclosed
in FIG. 9 comprises two basic operations: a process for
continuously producing void-free, gas occlusion-free PC compounds,
and a process for continuously casting and molding the void-free PC
compounds. The latter process includes steps for curing molded
compounds, and for automatically de-molding cured parts. Catalyzed,
void-free PC compounds can be cast and molded into PC composites
immediately, or can be stored, with or without Stage III
condensation, for later input into the casting and molding
operation. In either case, the production line is designed to
prevent air contamination at every step of the process.
[0253] B. In-Process Quality Assurance
[0254] In-process quality assurance is an integral part of the
production line. As shown in FIG. 9, the process includes four QA
monitoring stations. QA Monitoring Station # 1 verifies that the PC
compound is suitable--e.g., void-free, air-free--for casting and
molding into finished articles. Assuming quality criteria are met,
a diaphragm-type pump, or similar air-free pumping system,
transfers the PC compound from the closed mixer in the PC
compounding line, into a closed-to-atmosphere, low pressure holding
tank. The holding tank is preferably equipped with an agitation
mechanism to prevent segregation of fine and coarse aggregates.
[0255] Quality Monitoring Station # 2 verifies that the PC
compound, after sotrage, is still suitable for molding and casting,
and a second diaphragm-type pump, or similar air-free pumping
system, transfers the unsolidified PC compound from the holding
tank to molding and casting apparatus (FIG. 10). The molding and
casting apparatus comprises an automatic, precision volumetric
dosing apparatus (FIG. 12), and a continuous, high speed,
automatic, air-free casting and molding apparatus (FIG. 13). The
dosing apparatus meters pre-defined, discrete volumes of catalyzed
PC compound, which are directly fed to the casting and molding
apparatus. During the casting and molding process, any remaining
replacement fluid condenses, and any excess resin is returned to a
PC material recovery system (FIG. 15).
[0256] Cast products are discharged from the casting and molding
apparatus, and conveyed to QA Monitoring Station # 3 for in-process
monitoring of porosity, aggregate structural homogeneity,
gas-phrase occlusions, and the like, using non-destructive testing.
One suitable non-destructive testing method is
spectral-analysis-of-surface-waves (SASW) described in Glenn J.
Rix, et al., 1284 Transportation Research Record 8 (1990), which is
herein incorporated by reference. Molded parts not meeting the
quality criteria are rejected, and the mold contents are returned
to the PC material recovery system.
[0257] Cast products meeting quality criteria are hardened by high
temperature curing in an air-free environment. The curing process
includes temperature ramping to optimize properties of finished
parts. Once hardened, the PC composites are de-molded (FIG. 14) and
sent to QA Monitoring Station # 4, where they are checked for
compliance with quality criteria including dielectric properties.
Parts not meeting the quality criteria are scrapped, and returned,
if economically justified, for recycling solids content in the
material recovery system. Parts meeting the quality criteria are
then visually inspected for surface quality and minor defects.
Visually acceptable parts proceed directly to finished product
marking and packaging for shipment; visually unacceptable parts are
sent to finishing/retouching for rework.
[0258] C. Continuous, High Speed, Automatic Air-Free Casting &
Molding Apparatus
[0259] FIG. 10 shows an isometric view of a continuous,
four-station, air-free casting and molding apparatus 100. The
apparatus has 90.degree. indexing, and is designed for automatic,
high speed production of molded PC composite parts. The casting and
molding apparatus 100 is comprised of a first 102, second 104,
third 106 and fourth station 108. The four stations are disposed on
a carousel 110 that rotates in a counterclockwise fashion on the
casting plate 112. FIG. 10 provides a snapshot of the casting and
molding apparatus 100 showing various operations that occur at each
station during one full cycle of the carousel 110. For example, the
first station 102 shows a mold removal operation as well as an
insertion of a resilient bottom cover 114 from a rotating dispenser
116; the second station 104 shows a volumetric dosing operation
(see FIG. 12); the third station 106 shows a mold thread up
operation; and the fourth station 108 shows a mold filling
operation (see FIG. 13).
[0260] The casting and molding apparatus 100 shown in FIG. 10 is
designed to produced fuse cut-out insulators, ranging in mass from
about two kg to about ten kg, and is designed to operate at 218
revolutions per minute, producing 571 insulators per hour. The
nominal residence time for each station is six seconds, and the
nominal indexing time is one second.
[0261] D. One-Piece Mold Apparatus and Method for Molding Inserts
into Product Body
[0262] FIG. 11 shows a schematic diagram of a one-piece mold
assembly 200. The mold assembly comprises a cylindrical canister
202 having an open end 204 and a closed end 206. The mold assembly
200 further comprises an expandable liner 208 having an inner
surface 210 and an outer surface 212. The expandable liner outer
surface 212 is cylindrical so that the expandable liner 208 can be
inserted into the open end 204 of the cylindrical canister 202, and
the shape of the expandable liner inner surface 210 defines an
outer surface of a molded PC composite (not shown).
[0263] The cylindrical canister 202 has an externally threaded
collar 214 near the open end 204. To form a given shape into an end
of the PC composite, the mold assembly 200 can contain a first
insert 216 near the closed end 206 of the cylindrical canister 202,
which is preferably an integral part of the expandable liner 208,
but can also be held in place with a fastener 218. A second insert
220 can be placed in the open end 204 of the cylindrical canister
202. In that case, the second insert 220 can be an integral part of
the bottom cover 114 of FIG. 10, or the second insert 220 can be
held in place with a fastener 218. The one piece mold can be
designed for any negative or positive angle surface configuration
in the molded part. FIG. 11 shows a negative angle design.
[0264] E. Precision Volumetric Dosing Apparatus
[0265] FIG. 12A through FIG. 12E show the operation of a precision
volumetric dosing apparatus 300 for air-free metering of
pre-defined, discrete volumes of catalyzed PC compound 302 (second
station 104 of FIG. 10). The volumetric dosing apparatus 300
comprises an upper piston 304, and an opposing lower piston 306, a
metering chamber 308, and a receiving chamber 310. The metering
chamber 308, which has a precision finished, smooth inner wall 312,
is connected to the carousel 110 of FIG. 10.
[0266] FIG. 12A shows the dosing apparatus 300 at the beginning of
a dosing cycle. In this position, the upper piston 304 is in its
fully retracted position. The resilient bottom cover 114 is held in
place by friction and is located near the end 314 of the lower
piston 306. The upper piston 304, the lower piston 306, and the
bottom cover 114 are in their respective standby positions.
[0267] FIG. 12B shows the next step in the dosing cycle. In this
step, the upper piston 304 moves vertically downward, sweeping
substantially all of the air from the metering chamber 308, which
exhausts through vents (not shown) adjacent to the bottom cover 114
standby position. The upper piston 304 continues to move downward,
until the end 316 of upper piston eventually contacts the bottom
cover 114. At that instant, the continuing downward motion of the
lower piston pushes the bottom cover 114 against the end 314 of the
lower piston 306, so that there is substantially no volume left for
air entrapment. The upper piston 304, the lower piston 306 and the
bottom cover 114 continue moving vertically downward as a group
until the lower piston end 314 is deep within the receiving chamber
310. At this point in the dosing cycle, the ends 314, 316 of the
pistons are surrounded by void-free PC compound 302.
[0268] Referring now to FIG. 12C, the upper piston 304 alone begins
to move vertically upward. Because of higher upstream pressure,
fresh PC compound 302 enters the receiving chamber 310 through an
opening 318.
[0269] As shown in FIG. 12D, the upper piston 304 continues to move
vertically upward creating a vacuum urging material after it. When
the end 316 of the upper piston 304 reaches a pre-selected and
adjustable start position 320 along the length of the metering
chamber 304, the lower piston 306 and the bottom cover 114 begin to
move upward. The upper piston 304, the bottom cover 114, and the
lower piston 306 continue to move upward at the same speed until
the end 316 of the upper piston 304 reaches a preselected and
adjustable stop position 322 along the length of the metering
chamber 308. During the latter stroke, the movement of the lower
piston 306 closes the receiving chamber opening 318. The distance
from the stop position 322 to the bottom 324 of the metering
chamber 308 determines the precise volume of PC compound 302 for
each molded PC composite (not shown). Prior to a production run,
the start position 320 is adjusted so that, given the desired stop
position 322, the bottom cover 114 will stop in the correct
position.
[0270] Finally in FIG. 12E, the lower piston 306 is retracted
slightly to its standby position, so that the dosing apparatus 300
can be rotated counterclockwise 90.degree. to the mold thread-up
operation (third station 106 in FIG. 10).
[0271] F. Air-Free Mold Filling
[0272] FIG. 13A through FIG. 13D show the operation of a mold
filling apparatus 400 (fourth station 108 of FIG. 10).
[0273] FIG. 13A shows the position of the mold filling apparatus
400 at the beginning of the filling cycle. The mold filling
apparatus 400 is comprised of the one-piece mold assembly 200,
described in FIG. 11, and the metering chamber 308, which contains
void-free PC compound 302 adding during the volumetric dosing
operation (FIG. 12). In this embodiment, the one-piece mold
assembly 200 is attached to the metering chamber 308 during the
mold thread up operation (third station 106 OF FIG. 10), although
any suitable attachment method can be used. The mold filling
apparatus further comprises a ram 402, which is composed of a
piston rod 404 and piston head 406. The piston head 406 is mounted
on a bearing 408, and can therefore rotate independently of the
piston rod 404. The piston head 406 is in contact with the bottom
cover 114, which together support the slug of PC compound 302
contained in the metering chamber 308.
[0274] As shown in FIG. 13B, the one-piece mold assembly 200,
metering chamber 308, and the piston head 406 are rotated, driven
by an external drive mechanism 118 (shown in FIG. 10). The rotation
is increased to a certain rotational speed--which can vary
depending on the geometry of the metering chamber 308, properties
of the PC compound 302, etc.--where centrifugal forces push the PC
compound 302 outward and upward against the inner surface 210 of
the mold assembly expandable liner 208, so that the free surface
410 of the PC compound is no longer flat, but has a parabolic
shape.
[0275] While this rotation speed is maintained, vacuum is drawn in
a cavity 412 formed by the expandable liner 208 through an orifice
414 in the mold assembly 200, and the ram 402 is moved vertically
so that PC compound is pushed into the cavity 412. During this
process, the free surface 410 maintains its parabolic shape. The
advancing PC compound 302 pushes trace air in the mold cavity 412
upwards to the orifice 414. The PC compound 302 entrains little or
no air since it is highly compacted by the centrifugal forces, and
its free surface 410 remains virtually undisturbed. Furthermore,
very little air, if any, is entrapped between the expandable liner
surface 210 and the PC compound 302 because the large centrifugal
forces acting on the PC compound 302 result in a near zero contact
angle along the advancing edge of the PC compound 302. In addition,
excess resin and fines migrate to the free surface 410 during
rotation as the larger diameter aggregates are compacted under by
the centrifugal forces. When the mold filling process is complete,
the excess resin and fines are vacuum removed through the orifice
414 and are sent to the material recovery system shown in FIGS. 9
and 15.
[0276] As illustrated in FIG. 13C, vacuum and rotation are stopped,
and the PC compound 302 is compressed in the mold cavity 410 by
vertically advancing the ram 402. This compression step condenses
any trace replacement fluid, and ensures a void-free PC compound
302.
[0277] In the final step of the mold filling cycle, shown in FIG.
13D, the ram 402 is retracted, freeing the one-piece mold assembly
200 and the metering chamber 308 to index to the first station 108
of the casting and molding apparatus 100 (FIG. 10), where the mold
assembly 200 is removed.
[0278] G. One-Piece Recyclable Mold De-Molding Process
[0279] A solidified PC composite part 500 can be de-molded from the
expandable liner 208 by the method shown in FIG. 14A through FIG.
14C.
[0280] In the first step of the method, an expandable liner 208
containing the molded part 500 is attached to a pressure vessel 502
having an open end 504 and a hollow cylindrical cavity 506, which
can accommodate the molded part 500 as shown in FIG. 14A. A tapered
lip 508, which forms the open end 504 of the pressure vessel 502,
fits snugly within the mold cavity 412 formed by the expandable
liner 208. A rigid can 510 is placed over the expandable liner 208;
the rigid can 510 is dimensioned so that a gap 512 exists between
its inner wall 514 and the expandable liner 208.
[0281] Next, air pressure is applied for a second or two through an
orifice 516 in the pressure vessel 502, as can be seen in FIGS. 14B
and 14C. The air pressure inflates the expandable liner 208 against
the inner wall 514 of the rigid can 510, liberating the part 500,
which falls by gravity into the pressure vessel cavity 506. A pad
518 prevents damage to the part 500 by cushioning its fall. The
amount and duration of air pressure required for the de-molding
process depends on the size and shape of the molded part 500, the
elastic properties of the expandable liner 208, etc.
[0282] H. PC Compound Material Recovery System
[0283] A process flow diagram for a PC compound recovery system is
provided in FIG. 15. Catalyzed, but unsolidified PC compound
material, degassed resin, and fines from the continuous casting and
molding process are delivered to an unsolidified compound recovery
hopper. From their, material is fed to a conventional liquid/solid
separator, such as a centrifuge, where fines, fillers and resin or
"resin rich compound" is separated from large, resin-wetted solid
particles. The latter can be scrapped or reused in convention PC
products if desired.
[0284] The resin rich compound is conveyed to a recovery tank,
which also receives degassed resin and suspended fines from the
mold filling operations shown in FIG. 13. The largest particles are
then separated from the resin rich compound. The further refined
resin can be combined with fines, fillers, monomer, etc. and used
to make void-free PC composites.
[0285] The present invention can be implemented in many apparatus,
methods and processes to produce a variety of void-free compounds
and composites. Accordingly, the scope of the invention should be
determined by the claims and not limited to the preferred
embodiments described above.
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