Note: Descriptions are shown in the official language in which they were submitted.
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Method and device for producing composite materials comprising a core
consisting of metallic foam.
The invention relates to a method and a device for producing composite
materials comprising a core of metallic foam, in which a metallic bond exists
between one or more metallic surface layers.
Several types of composite materials with porous cores of metal and surface
layers or surface sheets of solid metal are known, as are methods for their
manufacture.
Known to art are; first, metallic panels with a core of honeycomb structures,
which consist typically of thin aluminum sheet and are bound to the surface
sheets by means of adhesives. Known as "honeycomb" panels, they are used for
various purposes, and more particularly for light construction.
Also known are composite materials in which a panel-shaped core of metallic
foam is bonded to surface layers or sheets. Such a composite sandwich material
is described in U.S. Patent 37 11 363. Both types of glued composite materials
have the disadvantage that they have relatively low thermal stability owing to
the
use of adhesives and are therefore unsuitable for constructions in which
junctions between components are performed by welding processes or other
soldering methods, in which high temperatures are employed.
In German Patent DE 43 18 540 A1 a method and a device for the manufacture
of a composite material is described in which liquid aluminum foam is applied
to
a preheated aluminum sheet and in which, by means of a heated control device,
shaped parts are produced by stamping the foam and sheet metal. This method
does in fact allow a metallic bond between sheet metal and metallic foam, but
has, however, the disadvantage that the size of the components is restricted
by
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the form and the surface layer can only be applied to one side of the metallic
foam body.
Another method is known from German Patent DE 44 26 627 C2. In this method,
a core of pulverized foaming metallic materials and at least one surface layer
of
solid material are metallically bonded and the core of this composite foamed
by
heating the entire component. This method has the disadvantage that, after the
foaming of the composite, the quality, pore size and uniformity of the
structure of
the metallic foam in the interior of the component cannot be controlled, or
can be
controlled only with great expense and effort. Further, the costs of this
method
resulting from the use of metal powder and other components as foaming agent
are very high. Overall, the energy consumption of this powder metallurgy
method
is high when compared with the production of metallic foam using smelting
metallurgy.
It is to this point that the invention described below responds.
The object of the invention is to provide a method and a device for producing
composite materials with a core of metallic foam by means of which the above-
mentioned disadvantages of the state of the art can be avoided with the result
that, in a continuous or semi-continuous process, high productivity and thus
comparatively cost-effective production of composite materials is possible.
Furthermore, a method and a device will be developed for the production of
panels of compound materials in which the metallic foam core is metallically
bonded with one or more cover layers, by this means achieving a higher thermal
stability of the composite as compared to glued composite materials.
A solution of this task according to the invention is described in Claims 1
and 2
for the method and Claim 6 for the device.
According to the invention, a cooled panel-shaped body consisting of metallic
foam, which has already been cured, is bonded to one or more heated cover
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;r layers by means of rollers, so that a metallic bond is formed between the
metallic
foam body and the cover layer or layers. In the embodiment of the method
according to Claims 1 and 2, the heating of the cover layer or layers takes
place
in one or two heating devices shortly before the bonding with the metallic
foam
body in the rolling process. To achieve a comparatively lower cost of the
composite body the metallic foam body preferably consists of metallic foam
manufactured by means of casting technology. The heating devices are capable
of heating the cover layers continuously during their passage to the
temperature
required for metallic bonds. The heating of the cover layers may be performed
by
means of electrical induction or by burners operated by gas or by some other
heating medium. The heated cover layers are conveyed to the roller slot in a
guide which is thermally insulating and is immediately adjacent to the heating
device.
The preheating of the cover layers before their entry into the heating device
is
ensured according to Claim 3, in that oxide layers and any residues of roller
oils
or rolling emulsion from the use of sheet metal, which may be drawn directly
off
coils, can be reliably removed. It is useful for the cover layers to be led
into the
cleaning devices and the heating device by a drive device with controllable
speed. The drive devices must be reversible so that in cases of interruption
of the
process or breakdowns it will be possible to clear the device. As soon as the
roller assembly has engaged the cover layer, the revolutions of the drive
devices
and the roller assembly must be adjusted so as to harmonize with each other.
Alternatively, the drive device from this point in time can be shut down, so
that
the roller assembly then draws in the cover layers.
It may be required to perform pre-treatment of the metallic foam bodies
according
to Claim 3 in different manners as a function of their size, type and finish.
If the
evenness of the surface in relation to the thickness of the cover layers is
sufficient to obtain a plane-parallel composite body after the rolling
process,
simple brushes may suffice. Where there is a thicker skin on the surface of
the
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metallic foam, a preparation by machining, for example by milling the surface,
may be necessary. This preparation may also be undertaken in continuous flow
by a device located upstream of the device according to the invention.
According to the invention, in the case of metal foam bodies produced by
casting
technology, the skin surfaces can also be smoothed out in a still pliable semi-
fluid
condition and provided with a texture. When a cover layer is rolled onto only
one
side of the metallic foam body, skin can be removed from that side only, and
the
skin on the other side further smoothed out in the rolling process.
The parameters of the rolling process should be set up so that a pressure is
exerted on a composite materials body such that only a small degree of
transformation takes place in the metallic foam.
According to the invention, a skin of the metallic foam body can be fused on,
on
the spot, by rolling on a woven wire mesh or wire netting according to Claim
5,
using wire material that has a higher melting point than the metallic foam
material. The woven wire mesh is pressed into the skin and inlaid as a
reinforcing
plane and metallically bonded with the metallic foam.
After the rolling procedure the composite panel can be heat-treated
continuously
or discontinuously in a heat chamber. The times and temperatures for
equalization according to Claim 4 can be very different, depending on the
materials.
Given an appropriate viscosity of the basic material of the metallic foam, a
limited
degree of ductility of the composite panel in all axes of the plane can be
achieved
when it is in the heated condition. To avoid repeating the heating of the
composite material, the devices required for cutting and forming can be
arranged
immediately after the device according to the invention, in a subsequent
production line. ,
The advantages aimed at with the invention are more particularly to be seen in
that with the method according to the invention, it is possible to produce
cost
~
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thermal
stability and ease of connecting the panels by means of welding and other
fusion
processes. Yet another advantage is that with the continuous process there is
the possibility of producing composite panels of large dimensions,
particularly in
length.
It is further advantageous that by means of the process according to the
invention and the device according to the invention, different combinations of
materials and structures of not only cover layers but also of metallic core
bodies
can be processed into a multiplicity of composite materials with specific
characteristics. Composite materials can be combined with different types and
materials of cores made from metallic foam, such as metallic sponge and
variable metallic cover layers, and such composite materials can be produced
in
large dimensions.
Thus it is possible, for example, to produce a composite material whose cover
layers consist of steel sheet and core of aluminum foam. This composite
material
has the advantageous property that the surfaces are highly resistant to
mechanical stresses yet the component has a low specific weight.
The execution of the process also allows simple control of uniformity and the
size
of the pores of the foam core, and thus ensuring a consistent quality of the
composite.
Further details, characteristics and advantages of the invention are disclosed
in
the following explanation of a typical embodiment.
For production of a light-construction composite panel, a particle-reinforced
aluminum foam produced by smelting technology using the process according to
the invention is combined with an aluminum cover layer. The aluminum foam
used has a density of 0.3 kg/dm3, while the density of the aluminum is 2.7
kgldm3. Figure 1 shows a microscope photograph of a bond between the
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aluminum sheet 13 and a cell of the aluminum foam 12. It can clearly be seen
that a part of the cell structure, which was cold at the start of the bonding
process, has been pressed into the aluminum sheet, heated at this point in
time
and thus soft. It can also be seen that both parts have fused with one another
and a metallic bond has been formed.
If we produce a composite panel of this kind with a thickness of the aluminum
foam core 12 of 15 mm and two aluminum sheets 13 each of 1.5 mm, the density
of the composite material is approximately 0.7 kgldm3. A solid aluminum panel
of
the same thickness would have a weight greater by a factor of 3.9, and the
stiffness of such a panel would be only marginally higher.
The composite panel can be linked together at the cover layers with other
components by means of suitable welding processes, such as WIG or laser
welding.
Since both components of the composite material consist of the same basic
material, the composite panel can be sent for metal recycling.
Such a light-construction composite panel offers many possibilities for use.
More
particularly, it can save weight in vehicles of all kinds and mobile devices
and
thus reduce energy consumption.
The device according to the invention for producing composite materials with a
core of metallic foam is explained in fuller detail by the schematic
representation
in Figure 2. Figure 2 shows a vertical section in the direction of the
production
flow through a typical embodiment of a device according to the invention for
the
production of composite materials with a core consisting of metallic foam. The
device consists in its infeed section of a transport device 2 for the metallic
foam
body 11, one or two cleaning devices 3 for cover layers 10, several suctions 5
for
the dust and impurities resulting from the cleaning of the cover layers 10 and
the
metallic foam body 11, one or more drive devices 5 for the cover layers 10 and
one or more surface treatment devices 1 for the metallic foam body 11.
~
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The transport device 2 can be a known roller path or a conveyer belt or a
combination of the two and may additionally be provided with a drive device,
not
shown. In the central section of the device are arranged one or two heating
devices 7 and one roller assembly 6. The heating device 7 is fitted on its
runout
end with a thermally insulating guide, which encloses the cover layers 10
until
shortly before the roller slot and prevents premature cooling of the cover
layers.
The roller assembly 6 can be fitted, similarly to known roller assemblies,
with
two- or four-roller sets. The runout section of the device according to the
invention consists of a heat chamber 8 and cooling devices 9.
The device according to the invention operates in such a way that the panel-
shaped, cooled metallic foam body 11 is moved by the transport device 2
through
the surface treatment device 1 into the roller slot of the roller assembly 6.
In the surface treatment device 1 there can be performed not only the cleaning
of
impurities and oxide layers, but also the metallic activation of the surfaces,
as
well as the treatment by machining of any existing skin of the metallic foam
body.
The surface treatment described can be performed simultaneously on both the
top side and underside of the metallic foam body or on one side only.
Similarly,
the treatment and bonding of the cover layers 10 to the metallic foam body 11
can be carried out on one or both sides. For the sake of simplicity, treatment
of
only one cover layer will be described in what follows.
A ribbon-shaped cover layer 10, which can be produced according to Claim 5, is
fed by drive device 6 through the cleaning device 3 and into the heating
device 7.
If the cover layer is fed virtually endlessly from a coil, which is not shown
in
Figure 1, the drive device 5 can also be used for drawing the cover layer 10
off
from an uncoiling device, not shown. The drive device 5 is likewise capable of
retracting the cover layer from the heating device 7 by rotating the drive
rollers in
the opposite direction.
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The cleaning device 3 removes any residues of preservatives or oxide layers
from the side of the cover layer 10 involved in the bonding with the metal
foam
body 11. In the heating device 7 the cover layers 10 are heated to the
required
temperature, as described in Claims 1 and 2, distributed uniformly over its
entire
width. To prevent rapid cooldown, the heated ribbon is led through a closed
and
thermally insulated channel to the vicinity of the roller slot.
Cover layer 10 and metallic foam body 11 come together just before the roller
slot. They are acquired by the rotating rollers of the roller assembly 6 and
in the
roller slot the compression between the components is sufficiently great to
bond
them metallically together into a composite material.
To ensure an even speed of the metallic foam body 11, during the rolling
process
cover layers 10 and the roller jacket surfaces, and the drives of drive device
5,
transport device 2 and roller assembly 6, must be controlled so as to
harmonize
with each other. To ensure the specific required temperature of the cover
layers
according to Claims 1 and 2, it may also be necessary to control the output of
the heating devices 7 as a function of roller speed.
After they leave the roller assembly 6, the composite panels may require
tempering to stabilize the composite. In the heat chamber 8, which is located
directly following the rolling device, the composite material can be heated to
a
specified equilibrium temperature or simply kept warm for a specified period
of
time. The thermal chamber 8 and the cooling devices 9 are controllable and
permit a variable heating, holding and cooldown of the composite material.
In a preferred embodiment, the cooling device 9 operates with air, whereby the
speed of cooling is controlled by a variable air throughput. Furthermore, the
duration of the tempering and dwell time of the composite material in the
ongoing
process can be influenced by different lengths of the heat chamber 8. As well,
the transformation process described above is possible without use of the
cooling
device 9.
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LIST OF REFERENCE NUMBERS
1 Surface treatment device
2 Transport device
3 Cleaning device
4 Suction
Drive device
6 Roller assembly
7 Heating device
8 Heat chamber
9 Cooling device
Cover layer
11 Metallic foam body
12 Aluminum foam structure
13 Aluminum sheet
