CA2419924A1

CA2419924A1 - Method and device for producing composite materials comprising a core consisting of metallic foam

Info

Publication number: CA2419924A1
Application number: CA002419924A
Authority: CA
Inventors: Christian Steglich
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-08-25
Filing date: 2001-08-17
Publication date: 2003-02-19
Also published as: ATE280648T1; WO2002016064A1; DE50104320D1; EP1313583B1; DE10042569C1; EP1313583A1

Abstract

According to the invention, a refrigerated, plate-type body (11) consisting of metallic foam, which has already been hardened is bonded to one or several heated cover layers (10) by rolling (6), to create a metallic bond between t he metallic foam body (11) and the cover layer or layers (10). An installation for producing composite materials essentially consists of: cleaning devices (3); drive devices (5); heating devices (7) provided with thermally insulati ng guides for handling the cover layers (10); surface treatment devices (1) for treating the metallic foam body (11); a rolling frame (6) for bonding the cover layers and the metallic foam body, in addition to a thermal chamber (8 ) and refrigeration devices (9).

Description

' 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 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 ' CA 02419924 2003-02-19 ;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 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 ~

,~ effective composite materials for light construction that provide high 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 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.

g 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.

' CA 02419924 2003-02-19 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

Claims

1. Process for producing compound materials with a core consisting of metallic foam, in which a metallic bond is created between the core and one or more cover layers and the metallic .core body can consist of either closed-pore or open-pore metallic foam, characterized in that, shortly before bonding with the metallic foam body (11 ) by means of rollers (6) or some other panel-making process, one or more cover layers (10) are continuously heated during the passage of the cover layers (10) in one or two heating devices (7) to a temperature that is high enough relative to the specific flow curve of the material, that the cover layers (10) have a yield strength which is slightly less than the compression strength of the metallic foam body (11 ) when cooled approximately to ambient temperature.

2. Process for producing compound materials with a core consisting of metallic foam, in which a metallic bond is created between the core and one or more cover layers, and the metallic core body can consist of either closed-pore or open-pore metallic foam, characterized in that, in the case of cover layers (10) consisting of materials that have a higher melting temperature than the metallic foam core (11 ) and whose yield strength in heated condition exceeds the yield strength or compression strength of the cool metallic foam body, the cover layers (10) are heated to a temperature which is high enough so that at the contact surfaces between the cover layer (10) and the core (11) of the metallic foam during the rolling process (6), the outer cells of the metallic foam melt and the bond between cover layer and core is produced by adhesion or diffusion of the metallic foam material.

3. Process for producing composite materials with a core consisting of metallic foam according to Claims 1 or 2, characterized in that before the passage through the heating device (7) of the cover layers (10), their sides facing the metallic foam body (11) are cleaned to bare metal (3), and that the surface of the metallic foam body (11 ) is cleaned (1 ) and metallically activated, typically by means of brushes, shortly before binding with the cover layer or layers (10).

4. Process for producing composite materials with a core consisting of metallic foam according to one of Claims 1 to 3, characterized in that after the rolling process (6) the temperature of the composite material (10, 11 ) is held for a certain time at a level in which a diffusion and an equalization occurs between the materials of the cover layers (10) and the metallic foam body (11 ) and that subsequently the material bond undergoes a controlled cooldown.

5. Process for producing composite materials with a core consisting of metallic foam according to one of Claims 1 to 4, characterized in that one or more cover layers (10) may consist not only of sheet metal or structured flat metal parts but also of woven wire mesh or wire netting consisting of different metals.

6. Device for producing composite materials with a core consisting of metallic foam according to Claims 1 to 5, characterized in that it consists essentially of cleaning devices (3), drive devices (5) and heating devices (7) with thermally insulating guides for the handling of cover layers (1 ), of surface treatment devices (1) for the treatment of the metallic foam body (11 ), of a roller assembly (6) for bonding of cover layers and metal foam bodies, and of a heat chamber (8) and cooling devices (9), and in which both the last-named devices are arranged downstream of the roller assembly (6) and can be controlled, so that they provide a variable heating, holding and cooldown of the composite material.

7. Device for producing composite materials with a core consisting of metallic foam according to Claim 6, characterized in that a) surface treatment devices (1) are present on both sides of the metallic foam body (11) to be introduced between the two cover layers (10) and b) cleaning devices (3) are arranged for cleaning of the one side of the two cover layers (10) facing the metallic foam body (11 ) and c) heating devices (7) for the cover layers (10) are arranged downstream of the cleaning devices (3) and d) for mutually synchronized transport of the covering layers (10) and the metallic foam body (11), drive devices (5) for the covering layers and a transport device 2 for the metal foam body are provided and e) the binding of the metallic foam body (11) and of both sides of the cover layers (10) passing onto the metallic foam body takes place in the successive roller assembly (6).

8. Device for producing composite materials with a core consisting of metallic foam according to Claim 6 or 7, characterized in that the surface treatment devices (1) perform the metallic activation of the surfaces of the metallic foam body and, after treatment by the cleaning devices (3), the cover layers are heated in the heating devices (7) to the temperature required for bonding, distributed uniformly over the surfaces, and that during the rolling process the drives of the drive devices (5), transport device (2) and roller assembly (6) are adjusted to harmonize with each other and the heat output of the heating devices (7) is set as a function of roller speed.