U.S. patent application number 14/419696 was filed with the patent office on 2015-08-13 for microsphere-filled-metal components for wireless-communication towers.
The applicant listed for this patent is Dow Global Technologies LLC. Invention is credited to Mohamed Esseghir.
Application Number | 20150225815 14/419696 |
Document ID | / |
Family ID | 49230874 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150225815 |
Kind Code |
A1 |
Esseghir; Mohamed |
August 13, 2015 |
MICROSPHERE-FILLED-METAL COMPONENTS FOR WIRELESS-COMMUNICATION
TOWERS
Abstract
A wireless-communications-tower component being at least
partially formed from a microsphere-filled metal. The
microsphere-filled metal has a density of less than 2.7 g/cm.sup.3,
a thermal conductivity greater than 1 W/mK, and a coefficient of
thermal expansion of less than 30 .mu.m/mK. Microspheres suitable
for use in such microsphere-filled metal include, for example,
glass microspheres, mullite microspheres, alumina microspheres,
alumino-silicate microspheres, ceramic microspheres, silica-carbon
microspheres, carbon microspheres, and mixtures of two or more
thereof.
Inventors: |
Esseghir; Mohamed;
(Collegeville, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dow Global Technologies LLC |
Midland |
MI |
US |
|
|
Family ID: |
49230874 |
Appl. No.: |
14/419696 |
Filed: |
September 12, 2013 |
PCT Filed: |
September 12, 2013 |
PCT NO: |
PCT/US2013/059390 |
371 Date: |
February 5, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61707085 |
Sep 28, 2012 |
|
|
|
Current U.S.
Class: |
420/402 ;
420/528 |
Current CPC
Class: |
B22F 3/1112 20130101;
H01P 1/20 20130101; B22F 2003/1106 20130101; C22C 21/00 20130101;
C22C 1/08 20130101; H04W 88/08 20130101; B22F 3/1103 20130101; C22C
23/00 20130101 |
International
Class: |
C22C 1/08 20060101
C22C001/08; C22C 23/00 20060101 C22C023/00; C22C 21/00 20060101
C22C021/00 |
Claims
1. An apparatus, comprising: a wireless-communications-tower
component being at least partially formed from a microsphere-filled
metal, wherein said microsphere-filled metal has a density of less
than 2.7 grams per cubic centimeter ("g/cm.sup.3") measured at
25.degree. C.
2. The apparatus of claim 1, wherein the metal of said
microsphere-filled metal is selected from the group consisting of
aluminum, magnesium, and their alloys.
3. The apparatus of claim 1, wherein said microsphere-filled metal
has a thermal conductivity of greater than 1 watt per meter Kelvin
("W/mK") measured at 25.degree. C., wherein said microsphere-filled
metal has a linear, isotropic coefficient of thermal expansion
("CTE") of less than 30 micrometers per meter Kelvin (".mu.m/mK")
over a temperature range of -35 to 120.degree. C.
4. The apparatus of claim 1, wherein said microsphere-filled metal
has a density ranging from 0.6 to 2 g/cm.sup.3 measured at
25.degree. C., wherein said microsphere-filled metal has a thermal
conductivity ranging from 5 to 150 W/mK W/mK measured at 25.degree.
C., wherein said microsphere-filled metal has a linear, isotropic
CTE ranging from 8 to 25 .mu.m/mK over a temperature range of -35
to 120.degree. C.
5. The apparatus of claim 1, wherein said microsphere-filled metal
has a tensile strength ranging from 0.8 to 60 Kpsi.
6. The apparatus of claim 1, wherein said microsphere-filled metal
comprises microspheres selected from the group consisting of glass
microspheres, mullite microspheres, alumina microspheres,
alumino-silicate microspheres, ceramic microspheres, silica-carbon
microspheres, carbon microspheres, and mixtures of two or more
thereof.
7. The apparatus of claim 6, wherein said microspheres have a
particle size distribution D10 ranging from 8 to 30 .mu.m, a D50
ranging from 10 to 70 .mu.m, and a D90 ranging from 25-120 .mu.m,
wherein said microspheres have a true density ranging from 0.1 to
0.7 g/cm.sup.3.
8. The apparatus of claim 6, wherein said microspheres constitute
in the range of from 1 to 95 volume percent based on the total
volume of said microsphere-filled metal.
9. The apparatus of claim 1, wherein said
wireless-communications-tower component is selected from the group
consisting of a radio frequency ("RF") cavity filter, a heat sink,
an enclosure, a tower-top support accessory, and combinations of
two or more thereof.
10. The apparatus of claim 1, wherein said
wireless-communications-tower component is an RF cavity filter,
wherein at least a portion of said microsphere-filled metal is
copper and/or silver plated.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Provisional Application No. 61/707,085, filed on Sep. 28, 2012.
FIELD
[0002] Various embodiments of the present invention relate to
metal-based components for use on wireless-communication
towers.
INTRODUCTION
[0003] In the telecommunications field, it is expected that
bandwidth demand will increase annually across the world to support
new services and increased numbers of users, thus shifting wireless
systems to higher frequency bands. There is a trend in the industry
to move base-station electronics from the tower base to the upper
regions of wireless-communications towers (i.e., tower-top
electronics); this is an effort to reduce signal losses in
telecommunication cables connecting the tower top to the base
equipment. As increasing numbers of components are moved up the
tower, the weight of such components becomes a concern.
SUMMARY
[0004] One embodiment is an apparatus, comprising: [0005] a
wireless-communications-tower component being at least partially
formed from a microsphere-filled metal, [0006] wherein said
microsphere-filled metal has a density of less than 2.7 grams per
cubic centimeter ("g/cm.sup.3") measured at 25.degree. C.
DETAILED DESCRIPTION
[0007] Various embodiments of the present invention concern a
wireless-communications-tower component being at least partially
formed from a metal-based material. Such a metal-based material can
have certain properties making it suitable for tower-top
applications, including certain ranges for density, thermal
conductivity, and coefficient of thermal expansion, among others.
Such wireless-communications-tower components can include radio
frequency ("RF") cavity filters, heat sinks, enclosures, tower-top
support accessories, and combinations thereof, among others.
Metal-Based Material
[0008] As just noted, the wireless-communications-tower component
can be at least partially formed from a metal-based material. As
used herein, "metal-based" materials are materials comprising metal
as a major (i.e., greater than 25 weight percent ("wt %"))
component. In various embodiments, the metal-based material can
comprise one or more metals in a combined amount of at least 50, at
least 60, at least 70, at least 80, at least 90, or at least 95 wt
%. In some embodiments, one or more metals constitute all or
substantially all of the metal-based material. As used herein, the
term "substantially all" denotes a presence of non-described
components of less than 10 parts per million ("ppm") individually.
In alternate embodiments, the metal-based material can be a
composite of metal with one or more fillers, as described in
greater detail below, and may thus comprise one or more metals in
lower proportions (e.g., from as low as 5 wt % up to 99 wt %).
[0009] The metal component of the metal-based material can be any
metal or combination of metals (i.e., metal alloy) known or
hereafter discovered in the art. In various embodiments, the
metal-based material can comprise a low-density metal, such as
aluminum or magnesium, or other metals such nickel, iron, bronze,
copper and their alloys. In one or more embodiments, the
metal-based material can comprise a metal alloy, such as aluminum
or magnesium and their alloys. In certain embodiments, the
metal-based material comprises aluminum. In various embodiments,
aluminum constitutes at least 50, at least 60, at least 70, at
least 80, at least 90, at least 95 wt %, substantially all, or all
of the metal component of the metal-based material. Accordingly, in
various embodiments, the metal-based material can be an
aluminum-based material. Additionally, the aluminum employed can be
an aluminum alloy, such as AA 6061. Alloy 6061 typically contains
97.9 wt % aluminum, 0.6 wt % silicon, 0.28 wt % copper, 1.0 wt %
magnesium, and 0.2 wt % chromium.
[0010] As noted above, the metal-based material can have certain
properties. In various embodiments, the metal-based material has a
density of less than 2.7, less than 2.6, less than 2.5, less than
2.4, less than 2.3, less than 2.2, less than 2.1, or less than 2.0
grams per cubic centimeter ("g/cm.sup.3"). In such embodiments, the
metal-based material can have a density of at least 0.1 g/cm.sup.3.
Since the metal-based material can include polymer-metal
composites, as discussed below, density values provided herein can
be measured at 25.degree. C. in accordance with ASTM D792. For
non-polymer/metal-composite materials, density can be determined
according to ASTM D1505 by density gradient method.
[0011] In various embodiments, the metal-based material has a
thermal conductivity of greater than 1, greater than 2, greater
than 3, greater than 4, greater than 5, or greater than 6 watts per
meter Kelvin ("W/mK"). In such embodiments, the metal-based
material can have a thermal conductivity no more than 50, or no
more 100, no more than 180, or no more than 250 W/mK. All thermal
conductivity values provided herein are measured at 25.degree. C.
according to according to ISO 22007-2 (the transient plane heat
source [hot disc] method). In various embodiments, the metal-based
material has a linear, isotropic coefficient of thermal expansion
("CTE") of less than 50, less than 45, less than 40, less than 35,
less than 30, or less than 26 micrometers per meter Kelvin
(".mu.m/mK," which is equivalent to ppm/.degree. C.). In such
embodiments, the metal-based material can have a CTE of at least 10
.mu.m/mK. All CTE values provided herein are measured according to
the procedure provided in the Test Methods section, below.
[0012] In various embodiments, the metal-based material has a
tensile strength of at least 5.0 megapascals ("MPa"). In such
embodiments, the metal-based material can have an ultimate tensile
strength generally no greater than 500 MPa. Since the metal-based
material described herein also relates to polymer-metal composites,
all tensile strength values provided herein are measured according
to ASTM D638. For metal-only samples, measure tensile properties
according to ASTM B557M.
[0013] In various embodiments, the metal-based material can be a
foamed metal. As used herein, the term "foamed metal" denotes a
metal having a cellular structure comprising a volume fraction of
void-space pores. The metal of the foamed metal can be any metal
known or hereafter discovered in the art as being suitable for
preparing a foamed metal. For example, the metal of the foamed
metal can be selected from aluminum, magnesium, and copper, amongst
others and their alloys. In certain embodiments, the foamed metal
can be a foamed aluminum.
[0014] In various embodiments, the foamed metal can have a density
ranging from 0.1 to 2.0 g/cm.sup.3, from 0.1 to 1.0 g/cm.sup.3, or
from 0.25 to 0.5 g/cm.sup.3. In some embodiments, the foamed metal
can have a relative density of from 0.03 to 0.9, from 0.1 to 0.7,
or from 0.14 to 0.5, where the relative density (dimensionless) is
defined as the ratio of the density of the foamed metal to that of
the base metal (i.e., a non-foamed sample of an otherwise identical
metal). Additionally, the foamed metal can have a thermal
conductivity ranging from 5 to 150 W/mK, from 8 to 125 W/mK, or
from 15 to 80 W/mK. Furthermore, the foamed metal can have a CTE
ranging from 15 to 25 .mu.m/mK, or from 19 to 23 .mu.m/mK. In
various embodiments, the foamed metal can have a tensile strength
ranging from 5 to 500 MPa, from 20 to 400 MPa, from 50 to 300 MPa,
from 60 to 200 MPa, or from 80 to 200 MPa.
[0015] In various embodiments, the foamed metal can be a
closed-cell foamed metal. As known in the art, the term
"closed-cell" denotes a structure where the majority of void-space
pores in the metal-based material are isolated pores (i.e., not
interconnected with other void-space pores). Closed-cell foamed
metals can generally have cell sizes ranging from 1 to 8
millimeters ("mm").
[0016] In various embodiments, the foamed metal can be an open-cell
foamed metal. As known in the art, the term "open-cell" denotes a
structure where the majority of void-space pores in the metal-based
material are interconnected pores (i.e., in open contact with one
or more adjacent pores). Open-cell foamed metals can generally have
cell sizes ranging from 0.5 to 10 mm.
[0017] Commercially available foamed metals may be employed in
various embodiments described herein. For instance, suitable foamed
aluminum materials can be obtained from Isotech Inc, in either
sheeted or 3-Dimensional cast form. Such materials can also be
obtained from Foamtech.TM. Corporation, Racemat.TM. BV, and
Reade.TM. International Corporation, each in sheet form.
[0018] In various embodiments, particularly when an open-cell
foamed metal is employed, the foamed metal can present a surface
region or a portion of a surface region that is either (a)
non-foamed metal, or (b) coated with a polymer-based material. In
such embodiments, the foamed metal can thus present a surface that
is free or substantially free of defects (i.e., smooth). Such
surfaces can facilitate metal plating and permit formation of
components where smooth surfaces are desired, such as the case of
heat sink fins, where the desired strength may not be achieved with
a foamed structure alone. In addition, being of such thickness,
fins do not generally add substantial weight to the construction,
thus it may be desirable to retain a non-foamed structure or fill
(or at least partially fill) the void-space pores of the foamed
structure with a polymer-based material for added strength. When a
surface region is non-foamed, the non-foamed portion can have an
average depth from the surface in the range of from 0.05 to 5 mm.
An example of a suitable foamed metal having a non-foamed surface
region is stabilized aluminum foam, commercially available from
Alusion.TM., a division of Cymat Technologies, Toronto, Canada.
[0019] Additional approaches to improve thermal dissipation of the
foamed metal can be, for example, the use of air passages through
the foamed core to enable air circulation without affecting the
overall performance of the article, such as retaining a sealed
enclosure to protect enclosed components. This approach is
particularly useful in the case where non-foamed outer layers are
used, i.e., where the circulation occurs only in the core via
judiciously placed channels.
[0020] When a polymer-based material is employed to provide a
defect-free or substantially defect free surface, or to fill or at
least partially fill the foamed structure for additional strength,
such polymer-based material can be applied in a thickness ranging
from 0.05 mm to fully penetrating the foamed metal to form an
interpenetrating polymer-metal network. Examples of polymer-based
materials for use in these embodiments include thermoset epoxies,
or thermoplastic amorphous or crystalline polymers. In an
embodiment, the polymer-based material is a thermoset epoxy.
Polymer-based materials can be applied to a surface region, or made
to penetrate inside the structure of the foamed metal using any
conventional or hereafter discovered methods in the art. For
example, such application can be achieved via vacuum casting or
pressure impregnation, or insert molding with a thermoplastic
material under pressure. The polymer materials can themselves be
filled with appropriate fillers for density reduction, heat
strength, and/or thermal conductivity enhancements. Such fillers
may include silica, quartz, alumina, boron nitride, aluminum
nitride, graphite, carbon black, carbon nanotubes, aluminum flakes
and fibers, glass fibers, glass or ceramic microspheres, and
combinations or two or more thereof.
[0021] In various embodiments, the metal-based material can be a
microsphere-filled metal. As used herein, the term "microsphere"
denotes a filler material having a mass-median-diameter ("D50") of
less than 500 micrometers (".mu.m"). Microsphere fillers suitable
for use herein can generally have a spherical or substantially
spherical shape. The metal of the microsphere-filled metal can be
any metal described above. As noted above, the metal of the
metal-based material can be aluminum. Accordingly, in certain
embodiments, the microsphere-filled metal can be a
microsphere-filled aluminum.
[0022] In various embodiments, the microsphere-filled metal can
have a density ranging from 0.6 to 2 g/cm.sup.3. Additionally, the
microsphere-filled metal can have a thermal conductivity ranging
from 5 to 150 W/mK. Furthermore, the microsphere-filled metal can
have a linear, isotropic CTE ranging from 8 to 25 .mu.m/mK. In
various embodiments, the microsphere-filled metal can have a
tensile strength ranging from 0.8 to 60 Kpsi (.about.5.5 to 413.7
MPa).
[0023] Various types of microsphere fillers can be employed in the
microsphere-filled metals suitable for use herein. In various
embodiments, the microsphere fillers are hollow. Additionally, in
certain embodiments, the microspheres can be selected from the
group consisting of glass microspheres, mullite microspheres,
alumina microspheres, alumino-silicate microspheres (a.k.a.,
cenospheres), ceramic microspheres, silica-carbon microspheres,
carbon microspheres, and mixtures of two or more thereof.
[0024] In various embodiments, microspheres suitable for use herein
can have a particle size distribution D10 of from 8 to 30 .mu.m.
Additionally, the microspheres can have a D50 of from 10 to 70
.mu.m. Furthermore, the microspheres can have a D90 of from 25 to
120 .mu.m. Also, the microspheres can have a true density ranging
from 0.1 to 0.7 g/cm.sup.3. As known in the art, "true" density is
a density measurement that discounts inter-particle void space (as
opposed to "bulk" density). The true density of the microspheres
can be determined with a helium gas substitution type dry automatic
densimeter (for example, Acupic 1330, by Shimadzu Corporation) as
described in European Patent Application No. EP 1 156 021 A1. In
addition, microspheres suitable for use herein can have a CTE
ranging from 0.1 to 8 .mu.m/mK. Also, microspheres suitable for use
can have a thermal conductivity ranging from 0.5 to 5 W/mK. The
microspheres can also be metal coated.
[0025] In various embodiments, the microspheres can constitute in
the range of from 1 to 95 volume percent ("vol %"), from 10 to 80
vol %, or from 30 to 70 vol %, based on the total volume of the
microsphere-filled metal.
[0026] In one or more embodiments, the microspheres can optionally
be combined with one or more types of conventional filler
materials. Examples of conventional filler materials include silica
and alumina.
[0027] Commercially available microsphere-filled metals may be
employed in various embodiments described herein. An example of one
such commercially available product is SComP.TM. from Powdermet
Inc., Euclid, Ohio, USA
[0028] In various embodiments, the microsphere-filled metal can
present a surface region or a portion of a surface region that is
either (a) non-microsphere-filled metal, or (b) coated with a
polymer-based material. In such embodiments, the microsphere-filled
metal can thus present a surface that is free or substantially free
of defects (i.e., smooth), which can facilitate metal plating and
allow formation of components where smooth surfaces are desired
(e.g., heat sink fins). When a surface region is
non-microsphere-filled, the non-microsphere-filled portion can have
an average depth from the surface in the range of from 0.2 to 5 mm.
When a polymer-based material is employed to provide a defect-free
surface, such polymer-based material can be applied in a thickness
ranging from 50 to 1,000 .mu.m. Examples of and methods for using
polymer-based materials for use in these embodiments are the same
as described above with reference to the foamed metal.
Wireless-Communications-Tower Components
[0029] As noted above, any one or more of the above-described
metal-based materials can be employed to produce, at least in part,
a wireless-communications-tower component. As used herein,
"wireless-communications-tower component" denotes any piece of
electronic communications equipment, global positioning system
("GPS") equipment, or similar equipment, or a part or portion
thereof. Although the term "tower" is employed, it should be noted
that such equipment need not actually be mounted or designed to be
mounted on a tower; rather, other elevated locations such as radio
masts, buildings, monuments, or trees may also be considered.
Examples of such components include, but are not limited to,
antennas, transmitters, receivers, transceivers, digital signal
processors, control electronics, GPS receivers, electrical power
sources, and enclosures for electrical component housing.
Additionally, components typically found within such electrical
equipment, such as RF filters and heat sinks, are also
contemplated. Furthermore, tower-top support accessories, such as
platforms and mounting hardware, are also included.
[0030] As noted above, the wireless-communications-tower component
can be an RF filter. An RF filter is a key element in a remote
radio head. RF filters are used to eliminate signals of certain
frequencies and are commonly used as building blocks for duplexers
and diplexers to combine or separate multiple frequency bands. RF
filters also play a key role in minimizing interference between
systems operating in different bands.
[0031] An RF cavity filter is a commonly used RF filter. A common
practice to make these filters of various designs and physical
geometries is to die cast aluminum into the desired structure or
machine a final geometry from a die cast pre-form. RF filters,
their characteristics, their fabrication, their machining, and
their overall production are described, for example, in U.S. Pat.
Nos. 7,847,658 and 8,072,298.
[0032] As noted above, a polymer-based material can be employed to
provide a smooth surface on the metal-based material and/or as a
filler for the metal-based material. For example, epoxy composite
materials can be employed to coat at least a portion of the surface
of the metal-based material. Exemplary epoxy composites are
described in U.S. Provisional Patent Application Ser. No.
61/557,918 ("the '918 application"). Additionally, the surface of
the metal-based material and/or the polymer-based material can be
metalized, such as described in the '918 application.
[0033] In various embodiments, at least a portion of the
above-described metal-based material can be metal plated, as is
typically done for RF cavity filters. For example, a metal layer
such as copper, silver, or gold can be deposited on the metal-based
material, or intervening polymer-based material layer, via various
plating techniques. Examples of suitable plating techniques can be
found, for example, in the '918 application.
[0034] In an embodiment, the wireless-communications-tower
component can be a heat sink. As known in the art, heat sinks,
which can be a component employed in remote radio heads, typically
comprise a base member and a heat spreading member (or "fins"). The
heat spreading member is typically formed from a high conductivity
material, such as copper. In an embodiment, heat sinks fabricated
according to the present description can comprise a base member
formed from any of the above-described metal-based materials, while
employing a conventional heat spreading member. In various
embodiments, when a foamed metal is employed (particularly an
open-cell foamed metal), the base member can have a non-foamed
surface as described above.
[0035] In various embodiments, the wireless-communications-tower
component can be an enclosure that contains and/or protects
electronic equipment. Examples of such enclosures can be, for
example, an MRH-24605 LTE Remote Radio Head from MTI Inc.
[0036] In one or more embodiments, the
wireless-communications-tower component can be a support member,
such as fastening brackets or components used in making
platforms.
[0037] Specific components include, but are not limited to, antenna
mounts, support brackets, co-location platforms, clamp systems,
sector frame assemblies, ice bridge kits, tri-sector t-mount
assemblies, light kit mounting systems, and wave-guide bridges.
[0038] Fabricating the above-described
wireless-communications-tower component from the metal-based
materials described herein can be performed according to any known
or hereafter-discovered metal-working techniques, such as forming,
bending, die-casting, machining, and combinations thereof.
Test Methods
[0039] Density Density for composite samples is determined at
25.degree. C. in accordance with ASTM D792. For metal-only samples,
determine density according to ASTM D1505 by density gradient
method.
Thermal Conductivity
[0040] Thermal conductivity is determined according to ISO 22007-2
(the transient plane heat source (hot disc) method).
Coefficient of Thermal Expansion
[0041] CTE is determined using a Thermomechanical Analyzer (TMA
2940 from TA Instruments). An expansion profile is generated using
a heating rate of 5.degree. C./minute, and the CTE is calculated as
the slope of the expansion profile curve as follows:
CTE=.DELTA.L/(.DELTA.T.times.L) where .DELTA.L is the change in
sample length (.mu.m), L is the original length of the sample (m)
and .DELTA.T is the change in temperature (.degree. C.). The
temperature range over which the slope is measured is 20.degree. C.
to 60.degree. C. on the second heat.
Tensile Strength
[0042] Tensile property measurements (tensile strength and %
elongation at break) are made on the cured epoxy formulation
according to ASTM D638 using a Type 1 tensile bar and strain rate
of 0.2 inch/minute. For aluminum metal samples, measure tensile
properties according to ASTM B557M.
Glass Transition Temperature (Tg)
[0043] Measure Tg by placing a sample in a differential scanning
calorimeter ("DSC") with heating and cooling at 10.degree.
C./minute at a first heating scan of from 0 to 250.degree. C. to a
second heating scan of from 0 to 250.degree. C. Tg is reported as
the half-height value of the 2nd order transition on the second
heating scan of from 0 to 250.degree. C.
Examples
Example 1
Materials Comparison
[0044] A sample of foamed aluminum (51) is compared to conventional
aluminum (Comp. A), three epoxy composite compositions (Comp. B-D),
and a glass-filled polyetherimide (Comp. E) in Table 1, below. The
foamed aluminum is a 25.4 mm thick sample having a density of 0.41
g/cm.sup.3 and a primarily open-cell structure obtained from Cymat
Technologies, Ltd. The conventional aluminum is aluminum alloy
6061. The mixing, casting, and curing processes for the epoxy
composite compositions (Comp. B-D) are generally carried out as
described below. The glass-filled polyetherimide is ULTEM.TM. 3452,
a polyetherimide having 45% glass fiber filler, commercially
available from GE Plastics.
Comp. B-D Preparation Procedure
[0045] The terms and designations used in the following description
include: D.E.N. 425 is an epoxy resin having an EEW of 172, and is
commercially available from The Dow Chemical Company; D.E.R. 383 is
an epoxy resin having an EEW of 171 and is commercially available
from The Dow Chemical Company; "NMA" stands for nadic methyl
anhydride, and is commercially available from Polysciences;
"ECA100" stands for Epoxy Curing Agent 100, is commercially
available from Dixie Chemical, and ECA 100 generally comprises
methyltetrahydrophthalic anhydride greater than 80% and
tetrahydrophthalic anhydride greater than 10%; "MI" stands for
1-Methylimidazole, and is commercially available from Aldrich
Chemical; SILBOND.RTM. W12EST is an epoxy silane treated quartz
with D50 grain size of 16 .mu.m, and is commercially available from
Quarzwerke.
[0046] The requisite amount of filler is dried overnight in a
vacuum oven at a temperature of .about.70.degree. C. The epoxy
resin which contains anhydride hardeners are separately pre-warmed
to .about.60.degree. C. Into a wide mouth plastic container is
loaded the designated amount of warm epoxy resin, warm anhydride
hardeners, and 1-methyl imidazole which are hand swirled before
adding in the warm filler. The container's contents are then mixed
on a FlackTek SpeedMixer.TM. with multiple cycles of .about.1-2
minutes duration from about 800 to about 2000 rpm.
[0047] The mixed formulation is loaded into a temperature
controlled 500 to 1000-mL resin kettle with overhead stirrer using
glass stir-shaft and bearing with Teflon.RTM. blade along with a
vacuum pump and vacuum controller for degassing. A typical
degassing profile is performed between about 55.degree. C. and
about 75.degree. C. with the following stages being representative:
5 minutes, 80 rpm, 100 Torr; 5 minutes, 80 rpm, 50 Torr; 5 minutes,
80 rpm, 20 Torr with N.sub.2 break to 760 Torr; 5 minutes, 80 rpm,
20 Torr with N.sub.2 break to 760 Torr; 3 minutes, 80 rpm, 20 Torr;
5 minutes, 120 rpm, 10 Torr; 5 minutes, 180 rpm, 10 Torr; 5
minutes, 80 rpm, 20 Torr; and 5 minutes, 80 rpm, 30 Torr. Depending
on the size of the formulation to be degassed, the times at higher
vacuums can optionally be increased as well as the use of a higher
vacuum of 5 Torr as desired.
[0048] Warm, degassed mixture is brought to atmospheric pressure
and poured into the warm mold assembly described below. For the
specific mold described below some amount between about 350 grams
and 450 grams are typically poured into the open side of the mold.
The filled mold is placed standing vertically in an 80.degree. C.
oven for about 16 hours with temperature subsequently raised and
held at 140.degree. C. for a total of 10 hours; then subsequently
raised and held at 225.degree. C. for a total of 4 hours; and then
slowly cooled to ambient temperature (about 25.degree. C.).
Mold Assembly
[0049] Onto two 355 mm square metal plates with angled cuts on one
edge is secured on each DUOFOIL.TM. (.about.330 mm.times.355
mm.times.0.38 mm) A U-spacer bar of 3.05 mm thickness and silicone
rubber tubing with 3.175 mm ID.times.4.75 mm OD (used as gasket)
are placed between the plates and the mold is held closed with
C-clamps. Mold is pre-warmed in about 65.degree. C. oven prior to
its use. The same mold process can be adapted for castings with
smaller metal plates as well as the use of thicker U-spacer bars
with an appropriate adjustment in the silicone rubber tubing that
functions as a gasket.
TABLE-US-00001 TABLE 1 Materials Comparison for
Wireless-Communications-Tower Component S1 Comp. A Comp. B Comp. C
Comp. D Comp. E COMPONENTS Foamed Aluminum (wt %) 100 -- -- -- --
-- Aluminum* (wt %) -- 100 -- -- -- -- DER 383 (wt %) -- -- 20.03
18.16 -- -- DEN 425 (wt %) -- -- -- -- 19.21 -- SILBOND W12EST (wt
%) -- -- 62.5 66.0 62.5 -- Nadic Methyl anhydride (wt %) -- -- 8.64
7.83 18.10 -- Epoxy Curing Agent 10 (wt %) -- -- 8.64 7.83 -- --
1-methylimidazole (wt %) -- -- 0.19 0.17 0.19 -- Glass-filled
polyetherimide** (wt %) -- -- -- -- -- 100 PROPERTIES Density
(g/cm.sup.3) 0.4 2.7 1.827 1.891 1.740 1.7 CTE (.mu.m/m K) 21 23.4
N/D N/D 42 19/36 (FD/TD)*** Thermal Conductivity (W/m K) 9.3 180
0.999 1.156 1.045 0.3 Tg (.degree. C.) (DSC) -- -- 160 156 158 217
Operating Temperature (.degree. C.) >250 >250 Up to 140 Up to
140 Up to 140 Up to 200 Flame Retardant Yes Yes Yes Yes Yes Yes
Platable.sup..dagger. Yes.sup..dagger..dagger. Yes Yes Yes Yes
Difficult N/D = Not Determined *Typical 6061 alloy (not measured;
data reported obtained from www.efunda.com) **Properties not
measured; data reported obtained from GE product data sheet ***flow
direction/transverse direction .sup..dagger.Plating procedure
followed according to the description provided in U.S. Provisional
Pat. application Ser. No. 61/557,918 .sup..dagger..dagger.Foamed
aluminum with good skin finish provides a platable surface
[0050] As seen in Table 1, the foamed aluminum provides lower
coefficients of thermal expansion as compared to thermosets, while
maintaining adequate thermal conductivity at greatly reduced
densities compared to conventional aluminum.
Example 2
Foamed Aluminum Filled with Thermoset Epoxy
[0051] Cast a foamed aluminum block having dimensions of
2''.times.2''.times.0.5'' in a filled epoxy formulation and cure,
according to the following procedure. The epoxy formulation used is
DER 332+50/50 nadic methyl anhydride/Epoxy Curing Agent 100 (i.e.,
MTHPA) with 65 wt % SILBOND 126EST. The foamed aluminum foam is the
same as described above in Example 1. After mixing and degassing
the epoxy composition as described above, introduce the foamed
aluminum into the liquid epoxy mixture in the resin kettle and hold
in position using a stiffing blade to prevent it from floating.
Close the vessel and apply vacuum for 35 minutes as follows to
remove the air from the aluminum foam and force the liquid epoxy
into the metal pores: 10 torr for 10 min, 5 torr for 5 min, 10 torr
for 5 min, 20 torr for 5 min, and 30 torr for 5 min. Then bring the
vessel back to atmospheric pressure. Place a 550-mil thick U-spacer
into the mold, and pour about 1/2 of the degassed mixture into the
mold assembly (described above), the aluminum foam piece imbibed
with epoxy is then positioned in place and the remaining epoxy is
poured on the top. Conduct curing at 80.degree. C. for 16 hours,
then at 140.degree. C. for 10 hours, and finally completed at
200.degree. C. for 4 hours.
[0052] The resulting composite has an average density of 1.65
g/cm.sup.3, an average CTE ranging from 23.6 to 29.4 .mu.m/mK, and
a linear, isotropic thermal conductivity of 5.1 W/m K.
* * * * *
References