WO2011010874A2

WO2011010874A2 - Process for production of metal-foam bodies integrated in housings

Info

Publication number: WO2011010874A2
Application number: PCT/KR2010/004787
Authority: WO
Inventors: Thorsten Blume; Simon Brautigam; Frank Reining; Enrico Zein; Henrik Stadsgaard; Stefan Frohlich
Original assignee: Alantum Corporation
Priority date: 2009-07-23
Filing date: 2010-07-21
Publication date: 2011-01-27
Also published as: KR20120051032A; DE102009034390A1; DE102009034390B4; CN102470440A; WO2011010874A3

Abstract

A process for the production of a metal-foam body integrated in a housing is provided, which includes the following steps: the provision of a housing (30a, 30b); the provision of at least one layer of a lamellar metal foam (10); the application of a binding agent and a metal powder to the metal foam and/or to the inner wall of the housing (10); the forming of a metal- foam body (20a, 20b) from the at least one layer of metal foam (10), with the result that the metal-foam body (20a, 20b) has a base surface A that is dimensioned such that the metal-foam body (20a, 20b), when it is inserted into the housing (30a, 30b), touches an inner wall of the housing (10) at several points; the introduction of the metal-foam body (20a, 20b) into the housing (30a, 30b); and the heating of the housing (10) and the inserted metal foam (20a, 20b) to a temperature T_s =1,0000 °C. A metal-foam body integrated in a housing is also given.

Description

PROCESS FOR PRODUCTION OF METAL-FOAM BODIES INTEGRATED IN HOUSINGS

The present invention relates to a process for the production of a metal-foam body integrated in a housing, and to a metal-foam body integrated in a housing.

Various uses of metal foams in industry, for example the automotive industry, require metal-foam elements that are firmly integrated in a housing. Examples of such uses are catalysts, filters, mixers, or heat exchangers based on metal foams. Normally, to produce such housings with metal-foam bodies, the metal-foam body is first formed as a finished moulding, then inserted into a housing and soldered to the housing.

Alternatively, the use of a fibre mat (ceramic fibres) as a bearing element between the housing and the moulded body is also possible. However, these connections have the disadvantage that they are very temperature-sensitive, which causes problems for example when the metal-foam body is used within the framework of high-temperature applications, e.g., as an engine-proximate catalyst. If fibre mats are used, they result in additional costs. In addition, such fibres can lead to damage to health because of their carcinogenic properties when they enter the human lung.

During the production of the actual metal-foam bodies, a sintering process normally takes place, which generates a surface structure and mechanical and thermal resistance desired for the respective field of use. This sintering process generally takes place immediately after the metal-foam body is formed and hardened.

A process for producing metal/metal-foam composite components is disclosed in DE 101 27 716 A1. According to this process, a flat or moulded metal part is inserted into the hollow chamber of a casting mould, wherein the hollow chamber is delimited at least partially by the metal part.

A mixture of molten metal and propellant that is solid at room temperature is then inserted into the hollow chamber and foamed there.

However, this process is incompatible in connection with certain processes for metal-foam production, in particular with those in which a moulded body made of polyurethane foam is first produced, then coated with a metal layer, and the polyurethane foam is then burned out.

This process is incompatible in connection with certain processes for metal-foam production, in particular with those in which a moulded body made of polyurethane foam is first produced, then coated with a metal layer, and the polyurethane foam is then burned out.

It is therefore the object of the invention to provide a process for the production of a metal-foam body integrated in a housing, in which the described disadvantages of the prior art can be avoided.

Furthermore, it is an object of the invention to provide a metal-foam body integrated in a housing.

These objects are achieved according to the invention by a process according to claim 1 and a metal-foam body according to claim 11. Preferred embodiments are given in the dependent claims.

According to embodiments of the invention, a process for the production of a metal-foam body integrated in a housing comprises the following:

- the provision of a housing;

- the provision of at least one layer of a lamellar metal foam;

- the application of a binding agent and a metal powder to the metal foam and/or to the inner wall of the housing;

- the forming of a metal-foam body from the at least one layer of metal foam, with the result that the metal-foam body has a base surface A that is dimensioned such that the metal-foam body, when it is inserted into the housing, touches an inner wall of the housing at several points;

- the introduction of the metal-foam body into the housing; and

- the heating of the housing and the inserted metal foam to a temperature T_S = 1,000℃.

The metal powder is a so-called "sintering powder" which serves to give the metal foam temperature resistance and sufficient roughness of the surface structure. According to the embodiments of the invention, the step of sintering the metal powder and the metal foam to each other at the same time serves to form a secure connection between the metal-foam body and the housing in order to integrate the metal-foam body in the housing.

Because of the high temperatures that are necessary for the sintering procedure, a fixed connection between the metal-foam body and the surrounding housing is created at the same time during the heating. It has been shown that the adhesion created in this way between the metal-foam body and the housing also withstands the high temperatures that occur, for example close to a motor vehicle engine. Thus, a metal-foam body produced according to the above process integrated in a housing can also be used as a catalyst in the engine-proximate area.

The term "lamellar metal foam" means, within the framework of embodiments of the invention, flexible or inflexible planiform structures with thicknesses between 0.5 and 10　mm. Such lamellar metal foams are also called "sheets". To produce a layer of such a lamellar metal foam a process can be used, for example one in which a layer of foam made of polyurethane or a similar plastic is first produced. Then a metal layer is applied to the plastic foam, for example by means of the so-called "slurry process" or by means of electrodeposition. In this way, thin metal-foam sheets that can be used in the embodiments of the invention form after the plastic has been burned out.

The thin metal-foam sheets are further processed to metal-foam bodies in a subsequent process step. In principle, this can occur in various ways. One possibility for the production of bodies from the metal-foam sheets is to stack the sheets one on top of another. In this case, the base surface A of the metal-foam body to be generated can for example correspond to the base surface of the individual metal-foam sheets. This means that the finished metal-foam body is inserted into the housing perpendicular to the base surface of the individual sheets.

In an alternative embodiment, the metal-foam body can be generated by coiling at least one layer of lamellar metal foam. In this way, a cylindrical or elliptical metal-foam body is produced, the base surface A of which is substantially circular or elliptical.

The base surface A of the metal-foam body is dimensioned such that the metal-foam body touches the inner wall of the housing at several points along the periphery of the metal-foam body. This can for example be achieved by a metal-foam body having the same shape as the hollow chamber defined by the housing and by the sizes of the hollow chamber and body substantially matching (in other words to within a few micrometers or millimeters), with the result that the metal-foam body touches the inner wall of the housing at its outer periphery. Preferably, the metal-foam body touches the inner wall over the whole of its outer periphery in the longitudinal direction L of the housing.

The binding agent and the metal powder can for example be applied successively in this order or also simultaneously in the form of a mixture.

According to an alternative embodiment of the invention, the step of applying a binding agent and a metal powder includes the attaching of a mixture thereof to the inner wall of the tubular housing before the metal-foam body is pushed into the housing. This means that the housing is already prepared before the metal-foam body is introduced in the sintering and binding procedure, in other words when the inner walls of the housing are freely accessible. In addition, the mixture is also applied to the metal foam before its introduction into the metal housing, as described above. In this connection, it is to be noted that the expression "introduction", as used here, can mean for example insertion into the housing if it is a tubular housing. Alternatively, this expression can mean the placing of the body into the housing, for example if the housing is constructed of several shells (e.g. two half-shells).

The metal powder can for example be contained in the mixture in a proportion of approximately 10　wt% to 80　wt%. If the composition lies in the named range, on one hand, the correct consistency of the mixture for the deposition on the surfaces is guaranteed, and on the other hand, the concentration of both components is high enough to guarantee both the sintering process and the process of connection to the housing with sufficient intensity. According to a variation, the mixture that is applied to the inside of the housing can have a different composition from the mixture that is applied to the surface of the metal-foam sheets. In particular, the former mixture may contain a higher proportion of binding agent, while a higher proportion of metal particles is contained in the latter mixture.

The metal powder can contain at least two of the following metals as an alloy: iron, chromium, aluminium, and nickel. The sintering of an alloy of the named metals guarantees high temperature resistance of the metal foam sintered together with these materials, with the result that the produced metal-foam body integrated in the housing can for example be used as a catalyst in the high-temperature range.

The mixture is preferably formed as a viscous composition. This means that the mixture is present in the form of a liquid with high viscosity. In this way, dripping or flowing away of the mixture on vertical surfaces is avoided to the greatest possible extent. In addition, such a paste-like mixture is easy to deposit.

The temperature T_S can for example lie between 1,100℃ and 1,300℃. Unlike the prior art, in which the sintering and the connecting of the housing to the metal foam is carried out in different, separate steps, in connection with the embodiment of the invention, heating is necessary only once, resulting in particular in the saving of energy.

The temperature is preferably maintained over a period of at least approximately 50 minutes. It is thereby guaranteed that both the sintering procedure and the connecting procedure are completed.

The binding agent can for example comprise one or more of the following constituents: water, wax, solvent, and adhesive.

The task of the binding agent is to give the mixture the desired consistency. The binding agent should in particular have the following properties: a high viscosity (liquid) at approximately 20℃, good drying properties, and no toxicity.

A circular tube can for example be provided as a housing, wherein the metal-foam body in this case is preferably a metal foam with a circular or elliptical base surface A. The cross-section of the metal-foam body should be substantially the same as the internal cross-section of the housing. Such a configuration guarantees easy insertion of the metal-foam body into the housing, wherein in addition, in the case of circular cross-sections, because of the rotation-symmetrical formation of the base surface of metal-foam body and housing, the position of the metal-foam body does not have to be heeded during insertion. The expression "substantially the same" means, within the framework of the invention, that the two named cross-sections differ by only a few millimetres, and in particular, by only a few micrometers.

In order to adequately protect the housing from stress, at least the inner wall of the housing can be produced from high-grade steel. It is hereby guaranteed that during the subsequent working of the metal-foam body the inner surface of the housing remains substantially unaffected. In addition, a surface made of high-grade steel withstands the often extreme conditions such as prevail for example inside an exhaust pipe close to the engine.

A metal-foam body integrated in a housing can be produced with the process according to the invention, wherein the metal-foam body touches an inner wall of the housing at several points thereof and wherein the metal foam of the body is secured to the inner wall of the housing by means of a sintering process. In other words, the metal foam is sintered to the housing at those points where it touches the housing, whereby high temperature resistance of the connection is guaranteed.

As already mentioned, the housing can be a tubular housing with a circular or elliptical cross-section. In this case, the metal-foam body is preferably a cylindrical or elliptical body the outer contour of which is substantially the same as the inner contour of the housing.

The metal-foam body can for example be formed from iron, chromium, aluminium, or nickel, or an alloy thereof. These are preferred materials, in particular for the production of the catalyst, since they are relatively inexpensive and at the same time have sufficient resistance to chemically active ambient conditions.

In order to provide the unit comprising housing and metal-foam bodies integrated therein with sufficient resistance to extreme ambient conditions, it is to be preferred that at least the housing inner wall is produced from high-grade steel or coated with a layer of high-grade steel.

The metal-foam body integrated in a housing can be a metal-foam body that is for example formed as a filter or a catalyst. Such catalysts are often used in exhaust-gas systems, for example in a motor vehicle or in a filter system, where they are exposed to high temperatures. Because of the mentioned resistant connection, the metal-foam body integrated in the housing has a long life even under high stress.

A simple and inexpensive process for the production of a metal-foam body integrated in a housing is provided by the invention. The composite of the two components is characterized by high temperature resistance because of the connection, produced by a sintering procedure, between the components.

The invention is now described in more detail with reference to the attached drawing that represents non-limiting embodiments of the invention.

It is to be noted in this connection that the representations in the drawing are not necessarily to scale. Rather, to clarify one or more details, the true proportions may be distorted.

In the drawings there are shown in:

Fig. 1 a flowchart of a process for the production of a metal-foam body integrated in a housing;

Fig. 2 layers of lamellar metal foams that can be used according to embodiments of the process according to the invention;

Fig. 3 different shapes of metal-foam bodies that can be used in embodiments of the invention;

Fig. 4 the step of inserting different metal-foam bodies into a housing;

Fig. 5 possible shapes of metal-foam bodies that can be formed according to embodiments of the invention; and

Fig. 6 metal-foam bodies that are introduced into the housing in different positions.

A flowchart of an exemplary embodiment of a process for the production of a metal-foam body integrated in a housing is represented in Fig. 1. The process comprises a first step S10 that comprises the provision of a tubular housing and the provision of a layer of a lamellar metal foam.

In a next step S20, a binding agent and a metal powder are applied to the metal foam and/or to the inner wall of the tubular housing. First the binder and then the metal powder can be deposited on the at least one layer of metal foam. Alternatively, both components can be applied in the form of a previously prepared mixture. The application can be carried out for example by painting the surfaces of the individual layers. However, it is also possible to dip one or more layers of metal foam into the mixture.

There follows a step S30 of forming a metal-foam body from the at least one layer of metal foam. As already mentioned, this can be carried out by coiling a layer or by stacking several layers to form a three-dimensional body. The metal-foam body is dimensioned such that, when it is pushed or inserted into the housing, it touches the inner wall of the latter at several points, preferably over the whole of its outer periphery. Thus, there are sufficient contact points or surfaces between the metal-foam body and the housing.

If it is ensured that a sufficient quantity of metal powder and binder adheres to the metal-foam body produced in this way and the inner surface of the housing, then in a next step S40 the metal-foam body is introduced into the housing deep enough to rest on the place provided for it within the housing. The metal-foam body touches the inner wall of the housing at several points, preferably over the whole of its periphery.

In a further step S50, the housing together with the metal foam is heated to a temperature T_S of more than 1,000 C. The metal-foam body is sintered and a connection between metal-foam body and housing inner wall is produced.

As can be seen in Fig. 2, layers of metal foam 10 can be provided in various shapes. The shape of the metal-foam layers 10 can for example be rectangular or square, as shown under the reference number 10a, or round or oval, as shown under the reference number 10b. The shape of a segment of a ring is also possible, as represented under 10c. Binders and alloy powders are now applied, separately or as a mixture, to the surfaces of these layers of metal foam 10a, 10b, and 10c.

The forming of a metal-

foam body

20a or 20b from the individual layers 10 is shown in Figure 3. According to an exemplary embodiment that is pictured on the left in the representation, the metal-foam body 20a is formed by stacking several layers 10 one on top of the other. The representation constitutes a side view of the finished metal body, which means that its base surface A runs perpendicular to the image plane.

According to an alternative that is shown next to it on the right in the representation, the metal-foam body 20b can also be manufactured by coiling a layer of metal foam 10, or several layers. This representation is, unlike the previous one, a direct plan view of the base surface A. The metal-foam body 20b represented here consequently has the shape of an elongated cylinder.

In each case, because it is built up from flat metal-foam layers 10, the

body

20a or 20b contains the mixture of binding agent and metal powder (alloy powder) distributed at the inside.

As can be seen in Figure 4, the metal-

foam bodies

20a and 20b are introduced into correspondingly shaped

housings

30a and 30b. On the left in the representation of Figure 4, the housing 30a is shown with the metal-foam body 20a inserted therein, again in side view. It can be seen that the metal-foam body 20a touches the inner wall of the housing 30a along the entire length L.

On the right in the representation of Figure 4, a housing 30b with a circular cross-section corresponding to the base surface A of the metal-foam body 20b is provided. The inner contour of the tubular housing 30b corresponds approximately to the outer contour of the metal-foam body 20b. In this way, it is ensured that there is good contact between the inner wall of the housing 30b and the metal-foam body 20b. The outer contour of the metal-foam body should however not be so large that, when being inserted into the housing, it damages the inner wall of the same or that excessive force has to be applied to introduce the metal-foam body into the inside of the housing.

Naturally, cross-sectional shapes of the housing and metal-foam body other than that shown can also be chosen, for example a square or rectangular cross-section. If the cross-section shapes of the housing and the metal-foam body correspond to each other, it is thereby guaranteed that, given suitable dimensions, the peripheries of the metal-foam body and the inner wall of the housing are in contact with each other over the whole periphery of the latter. The

unit comprising housing

30a or 30b and the metal-

foam body

20a or 20b, respectively, introduced therein can now be placed in a furnace (not represented in the figure) for the sintering process.

Fig. 5 shows various base surfaces A of metal-foam bodies that can be used within the framework of the invention. As can be seen, because of the layered structure comprising lamellar layers, almost any base surfaces are possible, for example rectangular, round, oval, or tri-oval. Because of the flexibility or bendability of the metal-foam layers, coiling into metal-foam bodies is also possible, as described above.

Possible positions of a metal-foam body 20a made up of several layers 10 inside a housing 30a are shown in Fig. 6. As the figure shows, the metal-foam body 20a can either be inserted such that the base surfaces of the layers 10 extend perpendicular to the side walls of the housing 30a (shown on the left in the figure), or such that the base surfaces of the layers 10 each extend parallel to the side walls of the housing 30a (shown on the right in the figure).

Claims

A process for the production of a metal-foam body integrated in a housing, featuring:

the provision of a housing (30a, 30b);

the provision of at least one layer of a lamellar metal foam (10);

the application of a binding agent and a metal powder (11) to the metal foam and/or to the inner wall of the housing (10);

the forming of a metal-foam body (20a, 20b) from the at least one layer of metal foam (10), with the result that the metal-foam body (20a, 20b) has a base surface A that is dimensioned such that the metal-foam body (20a, 20b), when it is inserted into the housing (30a, 30b), touches an inner wall of the housing (30a, 30b) at several points;

the introduction of the metal-foam body (20a, 20b) into the housing (30a, 30b); and

the heating of the housing (30a, 30b) and the inserted metal foam (20a, 20b) to a temperature T_S = 1,000℃.
The process according to claim 1, characterized in that the binding agent and the metal powder are applied successively in this order or simultaneously in the form of a mixture.
The process according to claim 1 or 2, characterized in that the metal powder is contained in the mixture in a proportion of 10　wt% to 80　wt%.
The process according to one of the previous claims, characterized in that the metal powder contains at least two of the following metals as alloy: iron, chromium, aluminium, and nickel.
The process according to one of the previous claims, characterized in that the mixture is formed as a viscous composition.
The process according to one of the previous claims, characterized in that the following applies to the temperature T_S: 1,100℃≤T_S≤1,300℃.
The process according to one of the previous claims, characterized in that the temperature T_S is maintained over a period of at least 50　min.
The process according to one of the previous claims, characterized in that the binding agent comprises at least one of the following constituents: water, wax, solvent, and adhesive.
The Process according to one of the previous claims, characterized in that a tubular housing is provided as the housing and that a metal foam with a circular or elliptical base surface A is provided as the metal foam, wherein the cross-section of the metal foam is substantially the same as the inner cross-section of the tubular housing.
The process according to one of the previous claims, characterized in that at least the inner wall of the housing is produced from high-grade steel.
The process according to one of the previous claims, characterized in that the step of forming the metal-foam body (20a, 20b) comprises stacking of several layers of lamellar metal foam (10).
The process according to one of the previous claims, characterized in that the step of forming the metal-foam body (20a, 20b) comprises the coiling of at least one layer of lamellar metal foam (10) into a roll.
A metal-foam body integrated in a housing, wherein the metal-foam body (20a, 20b) touches an inner wall of the housing at several points thereof, characterized in that a metal foam is secured to the inner wall of the housing by means of a sintering connection.
The metal-foam body according to claim 13, characterized in that the housing is a tubular housing.
The metal-foam body according to claim 13 or 14, characterized in that it contains iron or nickel.
The metal-foam body according to one of claims 13 to 15, characterized in that at least the inner wall of the housing is formed from high-grade steel.
The metal-foam body according to one of claims 13 to 16, characterized in that the metal-foam body (20a, 20b) is a filter or a catalyst.