Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD FOR THE PRODUCTION OF METAL FOAM OR METAL-
COMPOSITE BODIES WITH IMPROVED IMPACT, THERMAL AND SOUND
ABSORPTION PROPERTIES
FIELD OF THE INVENTION
The present invention relates to the field of powder metallurgy. More
specifically, it
concerns a method of manufacturing foamable metal or metal-composite bodies
and
their use, particularly as lightweight and stiff material with improved
impact, energy,
sound absorption and heat retardant properties. It also preferably concerns
environmentally friendly and low cost material produced from recycled aluminum
alloys or scrap with broad range of chemical composition.
BACKGROUND OF THE INVENTION
Already known in the prior art, there is German patent no 4101630 (US patent
no
5,151,246) which describes a method for the production of porous semi-finished
products from aluminum and copper-based alloy powders. The method described
therein comprises the steps of mixing of an alloy powder with a foaming agent,
filling
a press container with the mixture, simultaneously heating the filled
container and
applying pressure at which the foaming agent does not decompose,
simultaneously
cooling and removing the pressure, disassembling of the container followed by
pushing of the solid briquette out of it, which is immediately heat treated to
produce
a porous body or is subjected to preliminary hot deformation via extrusion or
rolling
followed by heat treatment. A very narrow range of products in terms of sizes
and
shapes can be produced with such method since the weight of the briquette is 2-
5
kg. In addition, this method demonstrates a very low output because of the
prolonged
heating of the large size press container filled with the powder mixture. Even
in the
case where the powder mixture would be heated in a container having 100 mm in
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diameter and 400 mm in height, the heating operation would be economically not
feasible.
Also known, there is a method for the production of porous semi-finished
products
from metallic powders that incorporates different variants.
A first variant includes the steps of coating the bottom floor of a press
container with
a metallic layer free of foaming agent, covering the metallic layer with a
powder
mixture comprising a foaming agent, and then covering the layer of powder
mixture
with a second metallic layer free of foaming agent. The container is then
heated, and
hot compaction is carried out. The shape of the body produced can be changed
via
deformation. Then, the body is foamed for formation of a new body wherein a
high
porous foamed metallic layer appears between two metallic layers.
A second variant includes the steps of disposing a dense metallic disk in an
empty
press container adapted for extrusion and filling the container with a powder
mixture
containing a foaming agent. Then, the container with the powder mixture is
subjected
to heating followed by the application of a pressure of about 60 MPa. Due to
the
pressure, the central part of the hard metallic disk, which blocks the hole of
the press
die, begins flowing through this hole and ensures extrusion process. During
subsequent extrusion stages, the compacted powder mixture plastically deforms
and
flows through the die hole. Also in this case, the dense metallic layer covers
the
extruded powder mixture, which is ready for foaming. After foaming of this
combined
body the metallic layer covers a core consisting of high porous foam.
The combined billets produced via both variants can be further rolled in
sheets, and
due to a heat treatment temperature, can be transformed in a porous metallic
body
(US Patent 5,151,246, September, 1992, B 22 F 3/18, B 22 F 3/24).
Also known in the prior art, there is a process including the steps of mixing
of an alloy
powder with a foaming agent and rolling the mixture at high temperature (in
the
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range of about 400°C for aluminum) in several rolling passes.
Intermediate heating
of the prerolled material following the individual roll passes is a
significant measure
to largely avoid creation of edge cracks. This produces a bonding of metal and
propellant powder particles in the roller nip and forms a gas-tight seal for
the gas
particles of the propellant. This body can be transformed by heat treatment in
a
porous metallic body.
The disadvantages of these techniques are the limited possibility of
production of
semi-finished products, especially sheets of commercial sizes, low product
yield and
output, high manufacturing cost.
Also known in the general field of powder metallurgy, there are the processes
described in EP 0127312 and in US 4,820,141 (EP0271095). These documents
which do not concern the production of foam metal are given as examples of art
related to the present invention.
EP 0127312 discloses a process for the consolidation of metal powders into
slab
configuration in which the metal powder is encapsulated, heated and inserted
in a
containment die and is subjected to a rolling operation to consolidate the
powder.
US 4,820141 discloses a method for forming non-equilibrium and/or metastable
metallic or non-metallic powder, foil or fine wire material into solid body.
The method
disclosed comprises charging the material into a metal container, subjecting
the
metal container containing the material to rolling at a temperature at which
the
inherent properties of the material are maintained, and thereafter removing
the metal
container.
The method of the present invention is distinct from and overcomes several
disadvantages of the prior art, as will be discussed in detail below.
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SUMMARY OF THE INVENTION
In accordance with a first aspect, the present invention concerns a method for
the
production of metal chips comprising the steps of:
i) providing a mixture of a metal alloy powder with a foaming agent powder,
the foaming agent having a given decomposition temperature above which the
foaming agent decomposes into gas, and the powders comprising finely dispersed
solid particles;
ii) pre-compacting the mixture of step i);
iii) heating the pre-compacted mixture of step ii) to a temperature below the
decomposition temperature and at which permanent bonding of the particles can
occur;
v) hot compacting the mixture obtained in step iii) for producing a compacted
body made of a metal matrix embedding the foaming agent; and
vi) reducing the compacted body into metal fragments and thereby obtaining
foamable metal chips.
Preferably; the step i) of providing the metal alloy powders and the foaming
agent
powder comprises the step of:
-disintegrating metal scraps, metal particles or metal chips into the metal
alloy
powder.
According to one alternative, the method comprises, after step vi), the steps
of:
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-heating the foamable chips to a temperature below a liquidus temperature of
the metal alloy and sufficient to make the metal chips plastic; and
-extruding the heated metal chips for producing a foamable metal wire.
The foamable metal wire obtained can advantageously be cut into smaller
foamable
5 wire segments.
According to a second alternative used for producing porous pellets, the
method
preferably comprises, after step vi), the step of:
vii) heating the foamable metal chips obtained in step vi) to a temperature
above the decomposition temperature of the foaming agent.
In this second alternative, the method preferably comprises, prior to step
vii) of
heating the metal foamable metal chips, the step of mixing said foamable metal
chips
with other powders, for instance refractory material powders. More preferably,
prior
to mixing the foamable metal chips with the refractory material powders, the
method
comprises the steps of heating the foamable metal chips to a temperature below
a
solidus temperature of the metal alloy and sufficient to make the metal chips
plastic;
and shaping the metal chips into metal granules, for instance spherical
granules.
The shaping of the metal chips into spherical metal granules preferably
comprises
the steps of dispersing the heated chips as a monolayer on a flat heated
surface;
and applying a heated plate over the monolayer, and shaping the metal chips by
simultaneously applying pressure with the heated plate and performing circular
movement with the same.
In both alternatives described above, the method may further comprises, after
step
vi) of disintegrating, the step of classifying the metal chips by grain size.
The grain
sizes preferably ranges from 1,5mm to 40mm.
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The metal alloy powders used in the process are preferably aluminium alloy
powder.
It is however worth noting that any suitable metal alloy powders commonly used
in
the art , for example copper alloy powders can be used.
Also preferably, the step of v) of hot compacting is hot rolling.
The present invention also concerns the use of porous metal pellets as
described
above as fillers for a material selected form the group consisting of a
polymeric
material, a soundproof material, a fireproof material and a shock absorption
material.
The polymeric material is preferably a resin and even more particularly an
expandable resin.
According to a second aspect, the present invention also provide a method for
the
production of a dense metal product comprising the steps of:
a) providing metal pieces and disintegrating said metal pieces into smaller
metal particles;
b) mixing the metal particles with an additive having a decomposition
temperature that is greater than a solidus temperature of said metal
particles;
c) pouring the mixture of step b) into a closed volume metal shell having a
given thickness and providing the metal shell with at least one passage for
gases to
escape;
d) increasing the density of the metal shell by applying pressure;
e) heating the metal shell to a temperature above a temperature equal to said
solidus temperature of the metal particles minus 55°C more or less
5°C (for example
if the solidus temperature is 480°C, the metal shell will be heated at
a temperature
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above 480°C minus 55°C, that is to say above 425°C more
or less 5°C) and below
said decomposition temperature of the additive, and immediately applying
pressure
on the metal shell sufficient to compress the metal particles and to create
micro
shear conditions between the metal particles so as to obtain a dense metal
product.
The metal pieces are preferably made of recycled aluminium scraps. Advantages
of
the process in such case are the following: its environmental friendliness
since it
uses recycled material, its cost effectiveness since the recycled aluminum
scraps are
readily available at low price. Another advantage is the fact that the
chemical
impurities contained in the aluminum metal scraps work as useful additives,
which
provide advantageous predetermined properties to the final product.
The smaller particles of step a) are preferably metal chips or a powder of
finely
dispersed metal particles.
Preferably, the method comprises, prior to step c), the step of pre-compacting
the
mixture. More preferably, the pre-compacting is performed by vibration.
Also preferably, the additive is a foaming agent, preferably selected from the
group
consisting of TiH2 and CaC03 that decomposes into gas at a temperature greater
than the above-mentioned decomposition temperature. In this case, the method
further preferably comprises, after step e), a step of heating the dense metal
product,
with or without the metal shell, to a temperature greater than the
decomposition
temperature of the foaming agent, for obtaining a foam metal product.
In step e), the pressure is preferably applied by hot rolling the metal shell.
More
preferably, the hot rolling is performed with a compression force sufficient
for
obtaining a 95-100% dense metal product.
The closed volume metal shell used in step b) preferably comprises two
continuous
longitudinal main surfaces with side edges, and is deformable in a cross
direction.
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The two longitudinal surfaces can be obtained from two coils of metal strip as
will be
discussed further below. In this case the hot rolling of step e) is preferably
performed
by at least one roll moving along one of the surfaces of the shell. Most
preferably, the
shell is hot rolled between two rolls.
The continuous surfaces are preferably partially closed at their side edges so
as to
provide the at least one passage for metal to escape or leaving gases way to
escape
in longitudinal direction. The partial closing can made by a process selected
from the
group consisting of discontinuous welding, bending, clamping and bonding.
Alternatively, the closed volume metal shell can be obtained by providing a
flat or
special shape pan with a lid. In this case, step c) comprises the steps of
pouring the
mixture into the pan and closing the lid of the pan leaving the at least one
passage.
Such passages) can be obtained by discontinuously welding, bending, clamping
or
bonding the lid to the side walls of the pan or by providing perforation in
the shell
itself.
The step c) of increasing the density of the metal shell preferably comprises
the step
of cold rolling the metal shell.
According to a still preferred embodiment of the invention, the method
incorporates
mixing of powder aluminum alloys of various systems: AI-Cu-Mg-Si, AI-Mg-Si, AI-
Mg-
Cu-Si (cast alloys), AI-Cu-Mg-Mn, AI-Mg-Cu, AI-Zn-Cu-Mg, AI-Zn-Mg-Cu (wrought
alloys) with a foaming agent. In one variant the mixture obtained is filled in
a split
reusable mould, which is heated with the powder mixture. Heating of the powder
mixture is carried out at a temperature, which ensures sintering after cooling
to the
temperature 10-20°C below the solidus of most fusible eutectics. As a
result, the
powder mixture looses its flowability. After removing the bottom of the mould,
the hot
mould is placed on the container of a vertical press. The ram of this press
pushes the
sintered powder mixture out of the mould into the press container, then a
dummy-
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block is placed and hot compaction of the sintered powder mixture is carried
out at
a low specific pressure to produce porous (86-92 % relative density), and easy
breakable briquettes. Using highly efficient machines, the cooled briquettes
are
reduced to fragment-shaped chips with powder particles of 0.5-5.0 mm in size,
chemical composition of which conforms to that of initial aluminum alloy
powder with
uniform distribution of the foaming agent.
The method of the present invention can be used for production of porous metal
bodies for the parts and structural elements used in civil-engineering,
machinery,
automative and aircraft and other industries wherein combination of such
unique
properties of this material as high specific strength and rigidity, energy
absorption,
heat insulation and sound-proofing, light weight, incombustibility, buoyancy
and
absolute environmental acceptability are required.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and advantages of the invention will become apparent
upon
reading the detailed description and upon referring to the drawings in which
figures
1 to 7 are schematic representations of the sequence of steps of a method
according
to a preferred embodiment of the invention. The detailed description of each
figure
is as follows:
Figure 1 schematically represents the step of mixing of metal powders with a
foaming
agent powder;
Figure 2 represents the step of pouring the mixture into a reusable shell and
of
precompacting the mixture by vibration;
Figure 3 represents the step of sintering;
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Figure 4 represents the step of pushing a sintered briquette from a reusable
can into
press mould;
Figure 5 represents the step of compaction of the sintered briquette;
Figure 6 represents the step of reducing the body into foamable chips;
5 Figure 7a represents the step of hot rolling the mixture of powders in a
closed
volume metal shell, figure 7b is an enlarged view of the powder mixture at the
nip
formed by the two rolls, the micro-shear condition within the mixture of
powders is
illustrated with the arrows;
Figure 8 is a phase diagram of the powder alloy: AI-Si;
10 Figure 9 is a phase diagram of the powder alloy: AI-Mg-Cu-Mn;
Figure 10 represents the steps of continuous or batch rolling of chips or the
powder
mixture in a metal shell formed by two metal strips;
Figure 11 represents the steps of continuous rolling of chips or the powder
mixture
in a metal shell formed by two continuous metal strips; and
Figure 12 represents the steps of continuous rolling of chips or the powder
mixture
in a closed volume metal shell.
While the invention will be described in conjunction with example embodiments,
it will
be understood that it is not intended to limit the scope of the invention to
such
embodiments. On the contrary, it is intended to cover all alternatives,
modifications
and equivalents as may be included as defined by the appended claims.
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DESCRIPTION OF PREFERRED EMBODIMENTS
The purpose of the present invention is the production of complex and simple
shape
products out of continuous hat-rolled sheets of commercial sizes made from the
chips produced from hot-compacted briquettes. The technical result obtained
due to
realization of the invention incorporates a dramatic increase in product yield
(creation
of a waste-free technology), a reduction in manufacturing cost of porous
products,
broadening of the range of products in terms of their geometrical sizes,
mechanical,
thermal and acoustic absorption properties and density.
Referring to figures 1 to 6, the method of production of porous products from
aluminum alloys incorporates mixing of metal particles (1 ) including powder,
scrap
pieces, pellets, bits and/or chips of an aluminum alloy containing two or more
alloying
elements, for example, selected from the group consisting of: AI-Cu-Mg-Si, AI-
Mg-Si,
AI-Mg-Cu-Si (cast alloys), AI-Cu-Mg-Mn, AI-Mg-Cu, AI-Zn-Cu-Mg, AI-Zn-Mg-Cu
(wrought alloys), as well as pure metals (with or without additives) with a
powder of
a foaming agent (2), the foaming agent (2) having a decomposition temperature
exceeding that of solidus of the aluminum alloy powder matrix. The mixture (5)
obtained is filled in a split reusable mould (6) that is heated with the
powder mixture
(5), as shown in figure 3. Heating of the powder mixture (5) is carried out at
a
temperature that ensures liquid-phase sintering after cooling to 10-
20°C below
solidus temperature of the lowest melting point eutectic. As a result, the
powder
mixture now in the form of liquid phase sintered briquettes (12) loses its
flowability.
After disassembling of the mould (6), the hot mould is placed on the container
(14)
of a vertical press. The ram (13) of this press (14) pushes the sintered
powder
mixture (12) into the press container (14), then dummy-block is placed and hot
compaction of the sintered powder mixture is carried out at a low specific
pressure,
as shown in figure 5. The hot-compacted briquettes (15) produced show a
density
of 86-92 rel. %. These briquettes (15) compacted at a low pressure are porous
(8-14
rel. %) and brittle, thus easily breakable. Referring to figure 6, using
highly efficient
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machines, the cooled briquettes (15) are reduced to fragment-shaped chips (18)
with
chips particles of 0.5-5.0 mm in size, chemical composition of which conforms
to that
of initial aluminum alloy powder with uniform distribution of the foaming
agent.
Also preferably, the chips (18) are classified by grain sizes from 1.5 up to
40 mm,
preferably up to 5mm, each size fraction is mixed with fine refractory
material
powders passive to aluminum, then the mixture is filled in moulds and heated
in a
furnace up to a foaming temperature which exceeds the liquidus point by 50-
70°C;
after completion of the foaming process, the mixture is screened to separate
the
refractory material powders from porous chips.
According to another preferred embodiment of the invention, the chips produced
are
classified by grain sizes from 1.5 up to 40 mm, preferably up to 5mm, each
size
fraction is heated up to a temperature below the solidus point of the alloy by
10-
100°C and then dispersed as a monolayer on a flat heated surface and
then the
fragment-shaped chips are pelletized by circular movements of a heated massive
disle-shaped plate; then each fraction of the pellets produced is mixed with
fine
refractory material powders passive to aluminum and then the mixture is filled
in
moulds and heated up to a foaming temperature which exceeds the liquidus point
by
50-70°C; after completion of the foaming process the mixture is
screened to separate
spherical porous granules from the fine refractory material powder.
According to a further preferred embodiment, the chips produced are classified
by
grain sizes from 1.5 up to 40 mm, preferably up to 5mm each size fraction is
dispersed as a monolayer on a special base, heated from below up to a
temperature
of phase transition to liquid state; when it is examined visually that the
foamed pellets
reach the desired size, they are removed out of the furnace.
The foamed pellets (also called porous pellets) may then preferably be mixed
with
a resin and injected into the internal space of any structural element
comprising one
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or more hollow pieces. The resin is cured to increase stiffness and energy
absorption
of the structural element.
According to another aspect of the invention, the chips which are not screened
to
size fraction are used to form a composite block which contains a flat
metallic sheet
with special coating on the surface of which a layer of chips is dispersed
and, above
this layer, at a certain height, the second metallic sheet with special
coating, stamped
beforehand for the desired component, is located and after this, the composite
block
formed is heated in a furnace up to a foaming temperature which normally
exceeds
the liquidus point by at least 50-70°C and when it is examined visually
that the
foamed pellets reach the upper metallic layer, the block with foamed powders
is
removed out of the furnace and cooled. (To provide for heating of the block in
inert
atmosphere).
Preferably in this case, to ensure bracing between the sheets, they are
fastened
together by connecting cross-pieces which simultaneously play a role of
fastening
connecting elements.
Also preferably, the chips, which are not screened to size fraction, can be
used to fill
to the desired volume fraction the internal space of any structural element
comprising
one or more hollow pieces. The whole assembly is heated above a temperature of
transition from solid to liquid state of an ahoy to form porous filler (core).
According to a further aspect of the invention, the rolling of the heated
foamable
particles is conducted together and between two or more heated metal sheets to
produce a composite body. The produced composite body is heated above a
temperature of transition from solid to liquid state of an alloy to form a
multilayer
structure with porous core and metallic bonds between core and facings
Figures 7a shows the step of hot rolling a closed volume metal shell (48)
enclosing
a mixture of small particles of metal (21), preferably metal alloy powders
coming from
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recycled aluminium scrap, and a foaming agent powder. The metal shell (48)
with the
mixture is first heated in a heater (50), rolled between two rolls (22) where
micro-
shear conditions of the particles occur; and a semi-finished foamable dense
product
(41 ) is obtained at the exit of the rolling process. As can be appreciated,
in front of
the nip (21 ) formed by the two rolls (22), the mixture of particles is
substantially loose
or flowable. After being processed between the rolls (22), the mixture consist
of a
compacted foamable mixture (16) of powder alloy with foaming agent. This
compacted structure (16) is obtained by subjecting the particles (19) to micro-
shear
conditions, such micro-shear conditions being created thanks to the use of the
closed volume metal shell (48). As can be appreciated, in the nip formed by
the two
rolls (22) a zone of plasticity (17) is created followed by a zone of
elasticity (18). As
shown in figure 7b, the particles (19) in the zone of plasticity (17) are
subjected to
compression forces represented with arrow (52) and shear forces represented by
arrows (54).
According to a further aspect of the invention shown in Fig.10, the hot chips,
and/or
a hot mixture of aluminum powder and a foaming agent, are poured into a
thermostatic feeder (32), where increase in density and movement of chips
and/or
mixture is induced by vibration, and rolled between two metal strips supplied
by coils
(36) heated at the furnace (33) to a temperature of about 100°C higher
than the
temperature of the chips. The produced composite body (41 ) is heated above a
temperature of transition from solid to liquid state of an alloy to form a
sandwich
structure with porous core and metallic bonds between core and facings.
According to a further aspect of the invention shown in Fig.11, the hot chips,
and/or
a hot mixture of aluminum powder and a foaming agent, are poured into a
thermostatic feeder (32), where increase in density and movement of chips
and/or
mixture is induced by vibration, and rolled between two continuous metal
strips (40)
heated at the furnace (33) to a temperature of about 100°C higher than
the
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temperature of the chips. The hot-rolled sheets (23) produced are cut to
blanks,
which are fed to a heat treatment.
According to a further aspect of the invention shown in Fig.12, the hot chips,
and/or
a hot mixture of aluminum powder and a foaming agent, are poured into a
5 thermostatic feeder (32), where increase in density and movement of chips is
induced by vibration, then poured on a metal strip from the coil (36) moving
on a
roller table (43). The chips and/or mixture of powder are then covered by an
upper
metal strip from coil (37), moved to a machine (44) for forming a shell and
for joining
the edge of the lower and upper metal strips. A closed cross section metal
shell (48)
10 filled with chips and/or the mixture of powder is thus formed in that
machine (44).
The shell is then straightened and density of chips and/or mixture of powder
increased in a straightening machine (45) and heated in a furnace (46). The
heated
shell is then hot rolled in a rolling mill (47). The produced composite body
(41 ) is
heated above a temperature of transition from solid to liquid state of the
alloy
15 obtained with the original mixture of powder to form a sandwich structure
with porous
core and metallic bonds between core and facings.
Alternatively, the metal shell (48) from the shell forming machine (44) shown
in figure
12 may be cut to blanks so to form a closed volume metal shell (48). Such
closed
volume metal shell (48) is then processed, as described above, to be
straightened,
heated, hot rolled and heated to a high temperature to form a sandwich
structure
with a porous core.
The possibility of realization of the invention characterized by the above-
mentioned
set of the signs and the possibility of the realization of the purpose of the
invention
can be corroborated by the description of the following examples.
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Example 1
The example of the realization of the method for production of dense foamable
chips
is as follows.
AI-Mg-Cu-Mn aluminum alloy powder (a liquidus temperature of the alloy is 640-
645°C, a temperature of low-melting point eutectic is 505°C) of
300 kg in weight was
mixed with TiH2 foaming agent of 3.25 kg in weight (a decomposition
temperature
is 690°C and filled in a split mold of 340 mm diameter, 800 mm in
height with internal
space of 290 mm in diameter. Figure 8 shows a vertical cross section of the
phase
diagram of AI-Mg-Cu-Mn alloys. Hatched zone in this figure represents alloys
used
in the process. As can be appreciated, the average solidus temperature is
503°C and
the liquidus temperature is approximately 650°C. The powder mixture was
compacted by vibration to obtain a density of 1.75-1.8 g/cm3. Weight of the
mixture
in each mould was from 97 up to 100 kg. The powder mixture was heated at a
temperature of 510-515°C to ensure liquid-phase sintering after cooling
down to a
temperature of 480-485°C, the powder mixture lost its flowability.
After disassembling
of the mould, the hot mould was placed on the container of a 10 MN or 15 MN
capacity vertical press. The diameter and height of the container were 300 and
800
mm respectively. The ram of the press pushed the sintered powder mixture into
the
press container, then a dummy-block was placed and hot compaction of the
sintered
powder mixture was carried out at a low specific pressure of 140-200 MPa. The
hot-
compaeted briquettes produced showed a density of 86-92 rei.
°l°. After cooling the
briquettes were reduced on special machines to fragment-shaped chips.
Heating of the primary powders above a temperature of appearance of low-
melting
point eutectic by 10-20°C and subsequent cooling below this temperature
by 20-30°C
ensure development of liquid-phase powder sintering. The powder mixture in
this
state loses its flowability and can be easily pushed from the mould into the
press
container. The first source of appearance of extremely low hydrogen amounts is
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decomposition of TiFi2 at a heating temperature. The second source is surface
hydrogen appeared due to reaction of absorbed (H20 molecules) with aluminum
cations which diffuse through an oxide film. Surface hydrogen and hydrogen
formed
due to decomposition of TiH2 leave the porous briquettes partially, while the
largest
hydrogen amount is capable of dissolving in appeared low-melting point
eutectic.
Then, hot compaction operation at a low pressure of 140 or 200 MPa is carried
out.
Pressure applied to a sintered briquette is able to form only a porous
briquette. The
porous state is necessary only to facilitate production of the chips on
special
machines. The main operation i.e. hot compaction is a waste-free process.
If the heating of the primary powder mixture is performed at a temperature
wherein
the particles do not bond for example a temperature of 10-20°C below
that of low-
melting point eutectic formation, the particle will not bond and the powder
mixture
obtained will retain its flowability. Transportation of the disassembled mould
to the
press container will be impossible, a briquette structure will be loose.
Example 2
The example of realization of the method for production of porous semi-
finished
pellets from the foamable chips is as follows:
AI-Zn-Cu-Mg aluminum alloys powder (a liquidus temperature of the alloy is 630-
640°C, a temperature of low-melting point eutectic formation is
480°C of 210 kg in
weight was mixed with CaC03 foaming agent of 12 kg in weight (a decomposition
temperature is 720°C) and filled in a split mold of 340 mm in diameter,
800 mm in
height with internal space of 290 mm in~ diameter. Figure 9 shows surfaces of
crystallization (surfaces of liquidus) of the powder alloy AI-Zn-Cu-Mg
containing Zn-4,
5%, Cu 3,5-4,5%, Mg -negligible, AI-balance. The alloys used are in the AL
corner
of the diagram (small hatched zone) and have a liquidus temperature of
650°C.
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Solidus of these alloys is in the interval of temperatures of 510-
520°C.The powder
mixture was compacted by vibration to obtain a density of 1.75-1.8 g/cm3.
Weight
of the mixture in each mould was from 97 up to 100 kg. The powder mixture was
heated at a temperature of 490-500°C to ensure liquid-phase sintering
after cooling
down to 450-460°C and the mixture lost its flowability. After
disassembling of the
mould, the hot mould was placed on the container of a 10 MN or 15 MN capacity
vertical press. The diameter and height of the container were 300 and 800 mm
respectively. The ram of the press pushed the sintered powder mixture into the
press
container, then a dummy-block was placed and hot compaction of the sintered
powder mixture was carried out at a low specific pressure of 140-200 MPa. The
hot-
compacted,briquettes produced showed a density of 86-92 rel.%. After cooling,
the
briquettes were reduced on special machines to fragment-shaped chips.
To realise the method, the chips produced were graded into grain sizes of 2.0,
3.0,
4.0 and 5.0 mm, each size fraction was mixed with fine refractory material
powders
passive to aluminium, the mixture was filled in moulds, heated in a furnace at
a
foaming temperature which exceeds the transition temperature from solid to
liquid
state by 50-70°C; after completion of the foaming process, the mixture
was screened
to separate the refractory material powders from porous pellets. The porous
pellets
from 3.0 up to 10.0 mm in size and 0.3 up to 0.9 g/cm3 in density are a good
filling
agent for any shape of cases for energy absorbing components used in the
automotive industry.
An easier technique for realization of the chips of the same alloy, graded
into grain
sizes of 2.0, 3.0, 4.0 and 5.0 mm is discussed below. Each fraction was
dispersed
as a monolayer on a special base, heated in a furnace from below on overheated
melt of salt up to a foaming temperature; when it was examined visually that
the
foamed pellets reached the desired size, they were removed out of the furnace
and
cooled. The pellets had a hemispheric shape with radius from 5.0 up to 20.0 mm
and
a density from 0.4 up to 1.0 g/cm3.
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Porous pellets of this size and shape can find application for production of
volumetric
noise suppression and fire barrier components and also large-size shock
absorption
elements. Product yield is 100%.
Example 3
An example of the realization of the method for production of flat porous semi-
finished products is as follows.
AI-Mg-Cu-Mn aluminum alloy powder (a liquidus temperature of the alloy is 640-
645°C, a temperature of low-melting point eutectic is 505°C) of
30 kg in weight was
mixed with TiH2 foaming agent of 0.32 kg in weight and filled in 10 closed
volume
metal shells with length 500 mm, width 120 mm and thickness 10mm. The powder
mixture was compacted by vibration and a pass through the straightening
machine
to obtain a density of 1.8 - 2.0 g/cm3. Weight of the mixture in each shell
was from
2.9 up to 3.2 kg. Then the powder mixture in a shell was heated at a high rate
in a
furnace to a temperature 515-550°C and fed on a rolling mill on which
29 kg of 120x
1000 x 5 mm blanks with metal facing and foamable core were rolled. The blanks
were used for free foaming of sandwich panels. High-temperature heat treatment
was carried out by heating of the sheet blanks from below on overheated melts
of
salts. At the required point, the foaming process was stopped by quick removal
of the
foamed sandwich panel from the furnace when thickness was 24.5 mm. The size of
the panel with porous core was 122 x 1005 x 24.5 mm. The lower and upper
surface
of the panels was smooth. The density of the porous semi-finished products
produced was 0.96-1.07 g/cm3. Panels yield was 95%.
Although preferred embodiments of the present invention have been described in
detail herein and illustrated in the accompanying drawings, it is to be
understood that
the invention is not limited to these precise embodiments and that various
changes
and modifications may be effected therein without departing from the scope or
spirit
of the present invention.
