EP0588182B1 - Thermally and acoustically insulating composite element, manufacturing method thereof and its use - Google Patents

Abstract

In the case of a sound-damping and/or sound-insulating and heat-insulating element of lightweight construction, in which the cell walls (3a) of foamed pores or cells (3), forming a foam body (8), consist substantially of aluminium or an aluminium alloy, the foam body is formed by a workpiece (7) which is deformed by heating and has a compacted mixture of powdered aluminium (9) or a powdered aluminium alloy and powdered blowing agent (10) and, if need be, powdered aluminium oxides (11). Since the material is, to the greatest extent, a monomaterial, simple metal recycling is possible. <IMAGE>

Description

The invention relates to a thermally and acoustically insulating composite body in lightweight construction using a foam body and to a method for its production and its use.

Such composite bodies, the cell walls of which essentially consist of aluminum or an aluminum alloy, are already known from DE-A-2 735 153, but are only acoustically effective. They have the task of forming the greatest possible resistance to the passage of sound waves from one side to the other of the component, which is referred to as "sound-absorbing". In addition, such composite bodies occasionally also have the task of damping the formation of sound waves on one side of the component, that is to say of performing a "sound-absorbing" function, for which purpose the composite body directly with the sound-emitting element, for example a body panel, by pressing or gluing and connecting clips.

In another area, namely the production of impact energy Absorbent components of vehicles and light buoyancy bodies in, for example, the aerospace industry, it is also known (DE-B-4 018 360) to mix metal powder, in particular an aluminum alloy, with a gas-releasing propellant powder, for example titanium hydride, and this mixture in one to compact hot at high temperature to produce a foam body with at least predominantly closed cells. Subsequent shaping, for example by cold rolling, is also known.

In another known (WO 91/03579) foam production process, metal, for example an aluminum alloy, is fused with stabilizing particles, for example aluminum oxide, to a temperature above the liquidus temperature of the metal matrix. The foam is produced by generating gas bubbles in the melt and by cooling. However, the production costs of such foam bodies that can be used as acoustically absorbing panels and thermally insulating panels are relatively high.

In addition, it is known from DE-B-3 224 224 for example Exhaust mufflers to use sound-absorbing discs made of foamed ceramic, the interconnected pores of which serve to hold exhaust gas condensates. However, ceramic material is relatively rigid and its shape can no longer be changed easily after shaping and sintering.

Furthermore, it is known (US Pat. No. 4,713,277) to introduce a thickener into an aluminum melt while stirring. This thickener (metallic calcium) serves to stabilize the melt viscosity. After the addition of titanium hydride powder to the relatively low-viscosity aluminum melt, an intimate mixture is achieved with further stirring. Now the mixer is removed from the mold and this is tightly closed with a lid. Then a foam body is formed by the foaming process, which has essentially closed cells. The cavity walls of the closed mold define the outer configuration of the foam body. Cylindrical foam bodies of this type, which are provided with through holes, are used as sound-absorbing inserts in mufflers.

However, the foam components used primarily for sound insulation purposes mostly have plastics such as polyurethane (DE-OS 27 35 153). The cell walls represent more or less pliable cuticles. For special tasks it is also known to connect open-cell foam structures with those foam structures which are closed-cell or which are filled or impregnated with fillers. The manufacturing costs of such double structures are relatively high. This also applies to open-pore foam fleece (DE-PS 36 24 427). In addition, there are also problems with the disposal of constructions that are no longer usable such acoustically effective components are equipped.

Thermally insulating laminate elements are also known (DE-A-38 21 468 and DE-U-92 03 734). These laminate elements are partly also acoustically effective. These components are each made up of several different layers of one or more materials, that is to say in a complicated manner. Because they are not self-supporting, you need additional stiffening, usually in the form of an aluminum support plate. With the variants, which are made of different materials, there is also the problem of recycling.

The invention has for its object to improve the composite body of the type mentioned in such a way that with good acoustic effectiveness it also has good thermal insulation properties, is easy to manufacture, has lightweight construction features and offers advantages over other materials in disposal.

The invention is characterized in claim 1, and further embodiments thereof are claimed in subclaims. Claim 7 claims a preferred production method.

Preferred forms of training are also explained in more detail with the aid of the description of the figures.

In the acoustically effective and thermally insulating composite body according to the invention, the foam body is designed in a special way. The foam body is formed from a workpiece which has a compacted mixture of powdered aluminum or a powdered aluminum alloy on the one hand and powdered blowing agent or blowing agent on the other hand and, if required, powdered aluminum oxide compounds. The workpiece can For example, be prepared by the method described in DE-PS 40 18 360 and it has been shown that the use of that method, ie the circumvention of the method described in US Pat. No. 4,713,277, is acoustically more effective in producing the material Leads components. In addition to the fact that the separate production of an aluminum melt, which is difficult to stabilize, is avoided before the addition of blowing agent, the user is able to easily produce any molded parts, provided that such a workpiece is pressed from aluminum powder and blowing agent powder and possibly aluminum oxide-containing filler Starting material is used.

This compacted workpiece is placed, for example, in a mold, the cavity walls of which determine the outer contours of the finished foam body. However, the shape can be made from such that the top is open. The aluminum powder is melted by heating and the blowing gas or blowing gas is released when the blowing agent or blowing agent decomposes, which transforms the aluminum melt into a foam structure with preferably essentially closed cells. With the open design, the possibility of free foaming is given. By subsequent upsetting free, without thickness limitation, foamed workpieces, the normally relatively round to polygonal foam pores are flattened with increasing degree of compression and molded in an ellipsoidal manner or the cell webs fold in perpendicular to the direction of upsetting. This leads to an anisotropic heat conduction behavior, which leads to a reduction in the heat conduction in the workpiece thickness direction and a slightly increased heat conduction in the workpiece plane direction, ie, a higher thermal insulation of the workpiece.

In addition, it is also possible to insert such a mat-shaped pressed workpiece made of the aluminum blowing agent powder mixture into cavities between components and to heat the workpiece so that it inflates between the opposite walls of the components and essentially completely fills the intermediate space. In addition to the acoustically effective sound-absorbing task, such a component also acts as a vibration-damping unit that dampens the adjacent components and also stiffens the overall construction.

The invention therefore offers a simple possibility of forming composite bodies with both mechanical and acoustically damping or insulating functions. At the same time, the composite body according to the invention favors disposal, since it can be easily separated from other materials of the overall assembly and can be reused without the formation of harmful and polluting gases and vapors in the usual metal separation and processing process. It is therefore also possible to use recyclable aluminum materials for the production of the compacted workpiece and therefore of the sound wave damping or insulating and heat insulating component.

A blackening of the workpiece produced on one side leads to a significant increase in the emission coefficient and thus to an increase in thermal insulation.

In the process according to the invention according to claim 7, it is advisable to use powdered aluminum in large excess over the proportions of the blowing agent powder, in a ratio between 10: 1 and 1000: 1. It is advisable to add compounds containing aluminum oxide in proportions of 0-30% (based on the total amount of powder). In all cases, it should Blowing agents, as well as other constituents, are largely homogeneously distributed in the aluminum powder, unless certain areas of the workpiece from the powder mixture are to foam less when heat is applied. The powder mixture is compacted to the workpiece under a pressure of advantageously between 10 and 500 MPa. Temperatures in the range between 400 and 900 ° C should be used for heating and foaming.

The component according to the invention can also be cold-formed even after foaming in order to adapt it even better to certain space requirements.

The component according to the invention is particularly preferably used in motor vehicles and machine systems, specifically as a sound-absorbing partition and / or sound-absorbing cover for vibrating wall parts and / or sound-absorbing thermal insulation of the entire exhaust line.

It has been shown that components with cell walls made of aluminum or aluminum alloys of the foamed cells forming the foam form a multifunctional structural component which not only corresponds to the wishes of an acoustically good effectiveness, but also solves the above-mentioned object and also has other advantages brings: Apart from the ease of manufacture by foaming in particular aluminum powder and a gas-releasing blowing agent powder with sufficient heating, in particular directly in the hollow form, which corresponds to the outer contours of the component, the aluminum structure is dimensionally stable and therefore self-supporting, but also much better thermally insulating compared to compact aluminum . The total weight is relatively low in the extent of the void formation. Disposal can be done together with the other metal components aluminum in particular without separating. The very costly segregation of plastic parts is avoided, particularly when used in automobile construction. The result is a simple recycling process.

Figur 1

einen schematischen Querschnitt durch ein erfindungsgemäßes Bauteil;

Figur 2

einen vergrößerten Ausschnitt aus dem rechten oberen Bereich von Figur 1;

Figur 3

einen noch weiter vergrößerten schematischen Aufriß aus einem Teil des Bauelements und

Figur 4

schematisch die Stufen des Herstellungsverfahrens.

An embodiment of the invention is explained with reference to the drawing. Show:

Figure 1

a schematic cross section through an inventive component;

Figure 2

an enlarged section of the upper right area of Figure 1;

Figure 3

a further enlarged schematic elevation of part of the device and

Figure 4

schematically the stages of the manufacturing process.

FIG. 1 schematically shows in cross section part of a type of “front shell” which, with its curved outer side 2, faces the passenger compartment within a motor vehicle. The component consists of an abundance of hollow cells 3, the cell walls 3a of which, as shown in FIG. 3, consist of aluminum. While the surface 2 facing the passenger compartment has an essentially closed, non-porous, thin aluminum skin which extends to the edge part 5, the sound-generating engine compartment can face the open-cell inner side 1, so that the sound enters the cells 3 or in spaces 3c can penetrate between adjacent cells 3. The inherently rigid foam body 8 from the hollow cells absorbs part of the sound waves that pass through the openings 3b in the cell walls 3a and / or into the spaces 3c penetrate neighboring cells 3, which do not, as at the connection point 3c of adjacent cells 3, frit and / or fuse together in the heat used in the foam formation. The aluminum skin 4 and the edge part 5 of the component are formed, for example, by fusing or frying the cell walls 3a.

In order to avoid protruding contours or to accommodate support elements, the component according to the exemplary embodiment of FIG. 1 is provided on the inside 1 with recesses 6; For this purpose, the component has a zone B of less thickness at this point than in the other zones A.

The minimum thickness of the component should be 2 mm; the layer thickness of the edge part 5 of the component of FIGS. 1 and 2 is approximately 3 mm, while the layer thickness in the zones A is of the order of cm. The distribution of layer thicknesses, cell and cavity sizes and cell wall thicknesses depends on the functions of sound absorption. In many cases, it is advisable to alternate zones of very good sound absorption with zones per se of less good sound absorption, as a result of which very specific overlay functions can be formed.

According to FIG. 4, starting from aluminum powder 9 on the one hand and titanium hydride powder 10 on the other hand and optionally powdered aluminum oxide 11, a homogeneous mixture of these two or three powders is produced in a mixing process. About 100 grams of aluminum powder, 0.5 grams of titanium hydride powder and 25 grams of aluminum oxide are added.

After the powders 9, 10 and possibly 11 have been mixed well, the mixture in a compacting stage under a pressure of, for example, 50 MPa becomes that in FIG. 4 schematically in cross section shown workpiece 7 pressed together. In comparison to the layer thickness, this can have relatively large dimensions and can be designed like a mat or profile.

Now the workpiece 7 can be made like any other workpiece made of normal aluminum or aluminum alloy without additions using known machining methods, such as Bending, milling, cutting, drilling, punching, extrusion, can be brought into any two or three-dimensional shape 7a.

Finally, the workpiece 7 is foamed in a heating and deformation stage, for example within a hollow mold, to give the foam body 8 shown schematically in cross section in FIG. 4, which has an essentially open-cell foam structure of the cells 3, but can be covered on the outside with a thin skin 4, without significantly affecting the acoustic effectiveness. This property is very surprising since it could be assumed that the foam body would have 8 openings. In this example, a temperature of 750 ° C. is sufficient for heating in order to form a foam body 8 with an average porosity of approximately 80% and an average cell size of approximately 0.8 mm.

Claims (16)

1. A thermally and acoustically insulating composite body in light-weight construction, using a body (8) of foamed material, formed from a workpiece (7) being deformed via heating and comprising a compacted mixture of powdery aluminium or, respectively, an aluminium ally (9) and a powdery blowing or expanding agent (10) and optionally a powdery aluminium oxide compound (11), and comprising an average porosity of 60 to 90%.
2. A composite body according to claim 1,
   characterised in
   that a plurality of the cells (3) of the foamed body (8) is open-cellular.
3. A composite body according to claim 1 or 2,
   characterised in
   that part of the surface (2) of the foamed body (8) is coated with a substantially closed, non-porous, thin aluminium skin (4).
4. A composite body according to any of the preceding claim,
   characterised in
   that the foamed body (8) comprises zones (A) of larger thickness and other zones (B) of lesser thickness.
5. A composite body according to any of the preceding claims,
   characterised in
   that the foamed body (8) comprises an average pore or, respectively, cells size between 0.1 and 1.5 mm and/or a density between 0.3 and 2.0 g/cm³.
6. A composite body according to any of the preceding claims,
   characterised in
   that the foamed body (8) is blackened on one side.
7. A method for manufacturing a foamed body (8), wherein the powder (9) comprising aluminium or an alluminium alloy is mixed with a powder (10) of an expanding agent at a ratio between 10:1 and 1000:1 (Al powder:expanding agent powder) to form a substantially homogeneously distributed mixture and compacted via pressing under a pressure between 10 and 500 MPa to form the workpiece (7) and is subsequently foamed into an open-cell foamed body (8), at least on one side, via heating between 400 and 900°C,
   characterised in
   that the powder (9) comprising aluminium or an aluminium alloy and the expanding agent powder (10) is mixed with a powder (11) comprising aluminium oxide, that this is mixed at a proportion of up to 30% of the total powder mixture, and that heating is controlled such that there results an average porosity between 60 and 90% for the thermally and acoustically insulating foamed body (8).
8. A method according to claim 7,
   characterised in
   that the workpiece (7 or 7a) is heated in a substantially closed mould such that it completely fills the mould during foaming and deforms into the mould of a foamed body (8), while it is not absolutely necessary that the workpiece (7a) be adapted, in its mould, to the shape of the final foamed body (8) before foaming.
9. A method according to claim 7,
   characterised in
   that the workpiece (7 or 7a) is freely foamed and subsequently upset more or less strongly and thus is brought to the final thickness.
10. A method according to any of claims 7 to 9,
    characterised in
    that the foamed body (8) is further cold-formed.
11. A method according to any of claims 7 to 10,
    characterised in
    that the workpiece is blackened on one side via graphitizing.
12. Use of a structural element according to any of claims 1 to 6 as a sound-insulating component such as a partition wall, for instance, in motor vehicles, aircraft, ships or machine systems.
13. Use of a structural element according to any of claims 1 to 6 as a sound-absorbing cover for vibrating wall portions in motor vehicles, aircraft, ships or machine systems.
14. Use of a structural element according to any of claims 1 to 6 as a heat-insulating component in motor vehicles, aircraft, ships or machine systems.
15. Use of a structural element according to any of claims 1 to 6 as a sound-insulating or, respectively, sound-absorbing a n d heat-insulating component in motor vehicles, aircraft, ships or machine systems.
16. Use of a structural element according to any of claims 1 to 6 as a self-supporting structural element in motor vehicles, aircraft, ships or machine systems.

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