Note: Descriptions are shown in the official language in which they were submitted.
PROCESS AND METHOD FOR PRODUCING FOAMABLE METALS
TECHNICAL FIELD
The present invention relates to a process for producing foamable materials
and
foamed metal articles. More particularly, the present invention relates to
mixtures of
foamable metal materials produced from at least one metal powder and gas-
producing
blowing agents.
BACKGROUND OF THE INVENTION
The production of foamed metal articles is known in the art. There are a
variety
of patents and publications concerning the production of foamed metal
articles, devices
and processes for producing said articles, and the metal/foaming agent
mixtures used
therein. The number of applications for foamed metals is high, including, but
not limited
to, stiffening of hollow structures, sound and vibration dampening, inhibition
of energy
flows, and creation of decorative elements.
Current methods of closed-cell foamed metal article production, however,
typically result in cells that are irregular and coarse, often with the
"windows" of the gas
bubbles appearing to be fissured. In addition, prior art methods usually
result in a
substantial amount of unfoamed metal material at the base of the foamed metal
article.
Accordingly, there is a need in the art for an improved metal/foaming agent
mixture and process for the production of foamed metal articles, that results
in more
thorough and consistent cell formation in the foamed metal article.
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SUMMARY OF THE INVENTION
This invention is directed to an improved process for producing foamable and
foamed metal articles, and an improvement of the industrial properties of the
foamable
products and of the closed-cell foamed metal articles by comparison with the
prior art.
In one exemplary embodiment, the present invention comprises a process for
producing foamable metal articles, the process comprising producing a mixture
of at least
one metal powder and gas-producing blowing agents, and compacting the mixture
to a
semi-finished foamable product or article or precursor, wherein the gas-
producing
blowing agent mixture contains some combination of silicon powder and talc
powder (Si,
[H2Mg3(SiO3)4] or [Mg3Si4010(OH)2]).
In another exemplary embodiment, the present invention comprises a process of
producing a foamed metal article, the process comprising subjecting the
aforesaid
compacted mixture and/or fomable product to conditions (e.g., elevated
temperature,
and/or elevated or reduced pressure) effective to foam said mixture.
In yet another exemplary embodiment, the present invention comprises the
foamed metal articles produced by said processes.
Still other advantages of various embodiments will become apparent to those
skilled in this art from the following description wherein there are shown and
described
exemplary embodiments of this invention simply for the purposes of
illustration. As will
be realized, the invention is capable of other different aspects and
embodiments without
departing from the scope of the invention. Accordingly, the advantages,
drawings, and
descriptions are illustrative in nature and not restrictive in nature.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic illustration of a process for producing foamable metal
articles and foamed metal articles in accordance with an exemplary embodiment
of the
present invention.
Figures 2 and 3 show a cross-section of a foamed metal article produced in
accordance with one embodiment of the present invention.
Figure 4 shows a cross-section of a foamed metal article produced in
accordance
with prior art techniques.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Figure 1 shows an exemplary embodiment of a process for producing foamable
metal articles and foamed metal articles in accordance with the present
invention. At
least one metal powder 10 is mixed with a gas-producing blowing agent 12
containing
some combination of silicon powder and talc powder (Si, [H2Mg3(SiO3)4] or
[Mg3Si4010(OH)2]). While other gas-producing blowing agents (e.g., titanium
hydride,
carbonates, and hydrates) have been used for producing foamable metal
articles, the use
of the combination of silicon powder and talc powder is not known in the art.
The combination of the metal powder 10 and the gas-producing blowing agents
12 is blended 20 and compacted 30 to form compressed foamable metal articles
40 useful
for producing foamed metal articles 70. The foamable metal articles then may
be
exposed to elevated temperature 50, and/or elevated or reduced pressure,
effective to
cause the foamable metal article to foam. The material is then cooled 60, if
necessary.
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In an alternative embodiment, the foamable metal article is placed in a mold
and foamed
therein.
The foamed metal articles produced with the aid of the gas-producing blowing
agent 12 in accordance with the present invention, especially produced auto-
catalytically,
.. have a morphology differing from that of foams obtained using prior art
foaming agents
(for example, titanium hydride, magnesium hydride). The foamed metal articles
produced by the foamable metal articles/precursors obtained by means of the
processes
described herein have a very homogenous pore density distribution extending
into the
surface regions of the shaped foamed metal article, as seen in Figures 2 and
3. Figures 2
and 3 show an aluminum foamed product produced according to the present
invention
using 10% Silicon powder and 1% Talc powder as the gas-producing blowing
agents
mixture, and aluminum metal powder (percentages are by weight of the blended
mixture).
This represents a considerable advance over foamed metal articles formed using
prior art methods and prior art gas-producing blowing agents. An
example of an
aluminum foamed metal article produced using prior art techniques, using 1%
titanium
hydride as the gas-producing blowing agent, is shown in Figure 4. The
compaction and
foaming conditions were identical with the process used to produce the article
shown in
Figures 2 and 3.
Figures 2 through 4 show a cross-section of the respective foamed metal
articles,
cut transversely. The foamed metal article produced using titanium hydride
in
accordance with the prior art shows extensive compaction (i.e., a substantial
layer of
unfoamed material) of the base zone 30 along the bottom of the article (see
Figure 4).
The cell distribution in the foamed structure is very irregular, and the cells
themselves are
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mainly coarse, and some have risen. This results in a somewhat fissured
surface of the
metal article, where large gas bubbles of this type have "blown off' on the
surface.
In contrast, the foamed article produced in accordance with the present
invention
(shown in Figures 2 and 3) distinctly shows more uniform foaming. The
compacted base
zone 26 is only approximately 0.25 mm thick, a marked improvement over the up
to 10
mm thick base zone 30 shown in the prior art material (Figure 4). In addition,
the
number of cells per unit volume in the foamed article produced in accordance
with the
present invention is distinctly greater, specifically with preference for the
presence of
small cells 28. Irregularity of cells is distinctly less pronounced than in
the prior-art
article, and the openings are finer and more uniform.
Examination of the structures of the cells in the foamed articles shown in
Figures
2-4 reveals a peculiarity of the prior art metal foam (Figure 4). As seen in
Figure 4, the
openings in the "windows" of the gas bubbles frequently appear to be fissured
32,
whereas virtually no such sites are evident in the foam of the present
invention (Figures 2
and 3). This indicates that, at the time when the volume of the metal changed,
the
viscosity of the material foamed according to the prior art is less than that
of the material
foamed according to the invention. A possible reason for this is that titanium
hydride
increases the viscosity of the surrounding metal (in this case, aluminum),
while the gas-
producing blowing agent of the present invention has had a contrary effect.
It is possible to foam all fusible metals or metal alloys in accordance with
the
method described herein. In one exemplary embodiment, the metal powder
particularly
preferably employed for the purpose of the present invention is aluminum and
its alloys.
In this embodiment, the metal powder comprises essentially aluminum, and where
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appropriate, conventional alloying constituents including, but not limited to,
magnesium,
copper, and/or silicon.
Thus, it should be understood that the embodiments and examples have been
chosen and described in order to best illustrate the principles of the
invention and its
practical applications to thereby enable one of ordinary skill in the art to
best utilize the
invention in various embodiments and with various modifications as are suited
for
particular uses contemplated. Even though specific embodiments of this
invention have
been described, they are not to be taken as exhaustive. There are several
variations that
will be apparent to those skilled in the art. Accordingly, it is intended that
the scope of
.. the invention be defined by the claims appended hereto.
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