EP1419835B1 - Method and device for producing flowable metal foam - Google Patents

Abstract

Production of a flowable metal foam having a mono-modal distribution of the dimensions of the hollow spaces comprises feeding gas (5) into a metal melt (4) from inlet pipes (3) protruding into a metallurgical vessel (2), and forming bubbles (6) on the ends (31) of the pipes. Independent claim are also included for: (a) device for producing a flowable metal foam having a mono-modal distribution of the dimensions of the hollow space; and (b) flowable metal foam produced.

Description

The invention relates to a method for producing flowable metal foam of a particle-containing molten metal with monomodal distribution of the dimension of the cavities in this. More specifically, the invention deals with the preparation of metal foams, each with substantially the same pore volume for use in moldings with a special property profile. Furthermore, the invention relates to a device for producing a metal foam in the above embodiment.

Metal foam, in particular light metal foam, is increasingly being used in molded articles with a special property spectrum, whereby the different requirements must be met with high reliability. In other words: the moldings with low weight should have high stability under precisely defined mechanical stress and / or be deformable under overload with maximum energy absorption.

It is known to manufacture objects made of metal foam. For example, WO 01/62416 A1 describes a process for producing a foam body, after which a mold with foam is filled by collecting individual bubbles rising in the melt. However, this method, in which the gas bubbles are usually introduced and separated by means of a so-called "rotor impeller", has the disadvantages that, on the one hand, a slow mold filling takes place and therefore in a cooled mold wall the last formed body part often has a disadvantageously thick wall layer and, on the other hand, the Uncontrolled bubble size is formed differently, which often have the mechanical characteristics of such a created part or body have a large, usually unfavorable spread.

From EP 0666784 B1, a further method has become known, in which is a molding of the stabilized liquid foam metal by pressing the stabilized foam into a mold with a pressure. However, so that the cells of the foam formed can not be brought to a uniform size.

EP 1288320A2 discloses an apparatus and a method for introducing gas into a molten metal, in which a uniformity of the diameter of the respective individual bubbles and the size of the gas bubbles are controlled.

A monomodal distribution of the dimensions of the cavities of a shaped body of metal foam, and a method for producing the same, it is apparent from EP A 1266973A2 and EP 1354651A2, the latter also discloses a corresponding device.

However, all of the state of the art attributable manufacturing process of flowable metal foam have the common drawback that individual bubbles usually connect only at a merge and often form thickened gusset areas. Furthermore, if desired, a desired filling speed of a mold for obtaining a uniformly thick surface layer of the body or a preferred metal flow therein may not be achieved.

The known devices usually allow non-contiguous metal foam bubbles of the same size to be produced in such a way that, in view of a low specific weight with high mechanical characteristics of the part, the partitions between the cavities can be made thin and can perform favorable support functions.

The invention aims to avoid these disadvantages and has set itself the goal of providing a method of the type mentioned, by means of which a flowable metal foam with monomodal dimensions of the cavities in a foamable melt at the gas inlet is formed and further formed.

Furthermore, the invention has for its object to provide a generic device for the production of flowable foam for processing the same.

The aforementioned object is achieved in a generic method with the characterizing features of claim 1.

The advantages achieved by the invention are essentially to be seen in the favorable foam structure, because even at the emergence of the pores in the liquid foamable metal in the sequence form the intermediate walls of a foam formation, which walls form thin and geometrically the force effects accordingly. Depending on the pore sizes provided, the interfacial tension and the buoyancy of the bubbles for the formation of a voluminous foam formation, which is developed into a foam body, must be taken into account in relation to a discharge quantity of gas to be maintained within wide limits.

According to the invention it is important that the size of the individual bubbles or cavities in the foam formation by the choice of the distance of the entry pipes from each other and, as is known, by the geometric formation of projecting into the molten metal pipe ends according to the EP 1288320A2 is determined. In this way, advantageous conditions for a similar formation of the bubbles and a desired formation speed of the formation can be created.

Conveniently, when the foam formation is placed in a mold or mold and allowed to solidify therein to form a moldable article, a dense but extremely small thickness of the partial surface layer can be created with a foam core immediately adjacent thereto.

An advantageous precisely limiting stability of a lightweight component can be achieved if the introduction of the foam formation in the mold or mold after a substantially thin-walled solidification of the molten metal takes place on the mold inner wall.

The above object of the invention is achieved in a generic device with with the characterizing features of claim 4

The advantages of such a device are essentially due to the fact that bubbles formed on the feed tube can be placed against one another in at least one side region and form an intermediate wall, whereby the release criteria are reached directly in the given case and a follow-on bubble is formed. Thus, by means of a device according to the invention, a favorable accumulation of the cavities in the foamable metal is effected directly upon their formation and an advantageous geometric formation of the intermediate walls of the foam formation is achieved.

For providing and forming components with low weight and / or high energy absorption during deformation, according to the invention advantageously a flowable metal foam, consisting of a plurality of cavities formed by introducing gas in the range of several equally spaced into a foamable Melt protruding ends of dimensionally equal insertion tubes, which is created by a juxtaposition of parts of the respective growing surfaces of the foam bubbles and thereby inducing size-determining closure thereof with each further reshaping of cavities a monomodal distribution of the dimension of the cavities in a foam formation, used ,

In particular, a use of a foam formation for a production of light metal parts in the automotive or aerospace industry due to the precise adjustability of the mechanical properties of the parts due.

Fig. 1

Ansatz von Blasen an Eintragsrohren in einer schäumbaren Metallschmelze

Fig. 2

Blasenvergrößerung

Fig. 3

Ausbildung von Zwischenwänden

Fig. 3a

Detail

Fig. 4

Neuformierung von Blasen im Verband

Fig.5

Schaumformation

In the following the invention will be explained in more detail by means of schematic diagrams. Show it

Fig. 1

Application of bubbles to feed pipes in a foamable molten metal

Fig. 2

bladder augmentation

Fig. 3

Training of partitions

Fig. 3a

detail

Fig. 4

Reformation of bubbles in the dressing

Figure 5

foam formation

In Fig. 1, a so-called blowing a foam formation is shown schematically, wherein gas 5 is injected from a pressure chamber under a nozzle 21 of a metallurgical vessel 2 in a foamable melt 4 through feed pipes 3, wherein in the region of the projecting pipe ends 31 gas bubbles 6 are formed. By means of a gas pressure of the same level and the same inlet pipe and pipe end dimensions, equal sized bubbles 6 are formed according to the laws of physics, but the respective bubble size can be determined by different injection conditions, if appropriate.

From Fig. 2 is a gas bubble enlargement 6 in front of the tube ends 31 in a foamable melt 4 in a metallurgical vessel 2 can be removed.

Now, if bubbles 6, which adhere to the ends 31 of the inlet pipes 3, each have reached a certain size of the distance A of the blowpipes, and the surface 61 abuts those of a neighboring bubble, then usually creates an intermediate wall 7, as shown in FIG. 3 is shown. By a change in the local surface tensions in the region of the pipe ends 31, as a result of the substantially abruptly magnifying, intermediate walls 7 between the gas bubbles 6 in a foam containing molten metal containing 4 takes place, as shown in Fig. 3a, characterized by an angle direct inducing of Release criteria of a bubble series.

Because, as shown schematically in FIG. 4, a gas introduction into a molten metal is continued, a new formation of gas bubbles 6 occurs at the tube ends 31, 31 ', 31 ", 31"'. Due to the surface tensions of the gas bubbles 6 and the tendency to form a package with corresponding surface boundary angles of the cavities is usually a lateral displacement of a series of substantially equal bubbles 6 and a new formation of such in the interstices of the intermediate walls 7 a Cavity row.

Newly formed bubbles 6 grow, as shown in FIGS. 1 and 2, to a critical size at which intermediate walls 7 are again formed and release criteria (FIGS. 3, 3 a) are created substantially abruptly, forming a hollow space formation in FIG a melt 4.

Such a homogeneous cavity or blister formation 1 is shown schematically in FIG. 5, wherein this formation 1 can be shaped grape-shaped or large-volume depending on the number of feed pipes 3, which has significance for further development and final shaping of bodies.

As favorable for a stable similar formation of a foam formation 1, which can be replaced by buoyancy itself or by a change in the gas supply criteria of the pipe ends 31, it is given if these ends 31 are multi-row, preferably three rows, positioned equal einragend in the melt, said however, each successive row is offset laterally by half the distance A of the ends.

Due to the Archimedean law, an introduction of foam formations 1 in forms is possible in a simple manner, with a monomodal distribution of the dimensions of the cavities 6 with favorable shaping of the intermediate walls 7 according to the invention.

Claims (5)

1. A method for producing free-flowing metal foam of a particle-containing metal melt with a monomodal distribution of the dimensions of the cavities, gas (5) being introduced into a foamable metal melt (4) from at least two adjacent, similarly dimensioned feed pipes (3, 3', 3 ", 3"'), projecting in a salient manner into a metallurgical vessel (2), and bubbles (6) being formed in the said melt in the region of each of the projecting pipe ends (31), characterised in that, with the increase in size of the adjacent bubbles (6), the release criteria are brought about by regions of the bubble surfaces (61) abutting one another and with the forming of particle-containing intermediate walls (7), and thus a cohesive foam formation (1) is produced and this is developed further.
2. A method according to Claim 1, characterised in that the size of the individual bubbles (6) or cavities in the foam formation (1) is determined by the selection of the distance (A) of the feed pipes (3) from one another, the said selection determining the release criteria, and by the geometric design of the pipe ends (31) projecting into the metal melt.
3. A method according to Claim 1 or 2, characterised in that the foam formation (1) is introduced into a mould or ingot mould and allowed to solidify therein to form a dischargeable moulding.
4. A device for producing free-flowing metal foam with a monomodal distribution of the dimensions of the cavities, in which at least two feed pipes (3) for gas (5) project in a salient manner into a foamable melt (4), [are provided]¹ side by side at a distance (A) from one another, characterised in that at least one further feed pipe (3) is provided, equally spaced, but offset in relation to the connecting line of the first feed pipes, and the feed pipes (3) are designed so as to be dimensionally equal and the pipe ends (31) are arranged on one surface.
5. A device according to Claim 4, characterised in that the ends (31) of the feed pipes (3) are positioned in multiple rows, preferably in three rows, projecting equally into the melt (4), each subsequent row, however, being offset laterally by half the distance A of the ends (31).

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