EP1288320A2 - Apparatus and process for the manufacture of a metal foam - Google Patents

Abstract

The method entails introducing gas into a particle-containing, molten metal to produce a free-flowing metal foam with voids having a monomodal distribution of their dimensions. The metal foam is at least partially introduced into a casting die and is compressed under essentially all-round pressure. The liquid phase is then allowed to solidify. An Independent claim is also included for a lightweight molded part.

Description

The invention relates to a device for introducing gas into a melt foamable metal by means of at least one tube for the production of metal foam

Furthermore, the invention comprises a method for producing metal foam by Blowing gas into a foamable molten metal.

In the innovative technology are increasingly materials with new Property profile required. Such a material is a metal foam, the on the one hand, in comparison with a solid material, a much smaller, specific one Has weight and on the other hand, different mechanical properties and a has completely different material behavior.

For a production of metal foam materials are different methods known. For example, substances can be added to a molten metal and into These are distributed, which substances at the given melting temperature decompose the metal phase with evolution of gas. In the melt while the forming or the gas bubbles formed frozen and such a foam body created.

Also known are foaming processes in which gas under the surface of a molten foamable metal, a so-called liquid Composite material, introduced and created such a metal foam.

From WO 91/01387 or EP-483184 B1, for example, such continuous foam process has become known.

An introduction of gas into the liquid metal can also according to EP-545957 B1 means of a vortex, wherein in the thus formed and solidified foam material There are pores with different diameters, from which a little reproducible material behavior results. Adjusting the pore size or Size distribution in the foam body is not sufficient possible.

According to US 5,281,251 gas is introduced into the melt by means of a Entry device, the whirl-shaped and on the outside wing ends Has gas outlet openings. A similar embodiment of the Gas introduction means or a vibrating or oscillating nozzle is disclosed in US 5 334 236.

In order to achieve efficient foaming, it has also been proposed (EP-544291 A1), the liquid metal gas via a plurality of nozzles in the manner of a oscillating nozzle comb or by means of a vertical nozzle with it To add rotating propeller-type stirrer for turbulence of the gas bubbles.

All known devices for the production of metal foam by blowing from gas to a melt are the common disadvantages that pores or gas bubbles are made with large dimension differences and their size and size Size distribution are not adjustable to the desired extent. This results in often undesirable comparatively high specific weights and insufficient reproducible material behavior of the metal foam material.

Here, the invention seeks to remedy the situation and sets itself the goal of a device of to create the type mentioned above, with which gas in the form of approximately having the same volume, adjustable in size pores or bubbles in the Melt is einbringbar. Another object of the invention is the specification of a Method for creating a desired metal foam.

The goal is achieved in a generic device according to the invention in that the gas inlet tube projecting protrudes into the melt and at the projecting end has a gas outlet cross-section with an area of 0.006 to 0.2 mm and a tube end face of less than 4.0 mm ² .

The advantages achieved by the invention are essentially to be seen in that Gas inlet tube in the formation of pores for their specific size stable Bubble removal criteria are created.

Is in a foamable metal according to the prior art gas through a Bore introduced into a nozzle plate, then arises, as studies have shown a bubble, whereby in the sequence around the bore an extension of the Bladder adhesion area occurs. The time of the replacement and thereby in the Practice formed size of the bubble on the nozzle plate are not subject to strict and tight law, so that thus formed metal foam with bubbles, which have different diameter is formed. Are in the nozzle plate for example, two or more holes for a gas inlet into the liquid metal provided, the extension of the respective bladder adhesion area at the Plate surface progress so far that the individual bubbles to form a Oversize bubble, giving a desired foaming is opposite. As mentioned at the beginning, has already been tried, a targeted Gas bubble separation from the nozzle or a division of large gas bubbles by a Relative movement of the gas inlet opening in the metal or by swirling too achieve, but not sufficiently, a desired effect rendered.

By the inventive geometric design of the gas inlet tube can created the first desired and stable gas bubble removal criteria in the melt which have substantially the same single bubble volume and accordingly resulting formed metal foam.

The formation of the device can be made with advantage so that the Outlet opening of the gas introduction tube to an extent of at least the 5 times, preferably at least 10 times, the value of the largest Inner dimension of the outlet opening is formed protruding into the melt. In order to are particularly effective stable tear-off criteria of the bubbles in the melt reachable.

If, in a favorable manner, the gas inlet tube a circular gas outlet opening and has a pipe end edge or annular pipe face, are special Economical pipe end formations for controlling the gas bubble size can be created.

To a great stability with a small end face of the gas supply pipe and also To achieve a high durability of the device in the foaming operation, it can be advantageous if the projecting into the melt gas inlet tube at least in Area of the gas outlet end a kugelsegment-, truncated cone or having truncated pyramidal outer contour. It is advantageous, the outer contour the gas introduction tube so that the angle that the generator of the Stump surface with the axis of the gas inlet channel includes a value of less than 60 °, preferably less than 45 °.

Plant technology, but also with regard to the performance of the plant and the Product quality can also provide a substantial advantage if at least 2, preferably more than 2 gas inlet tubes, in particular each with the same mutual distance, preferably a value of greater than 10 times the Einrageausmaßes the outlet opening and the gas inlet tube in the Melting, in a replaceable nozzle in the melting vessel of Metal foam systems are arranged. Such is a provision of a large one high-quality foam in short periods possible, which may be added a pre-material intensive processing, especially of large parts, it is asked for.

Although with a device of the type mentioned above excellent results in the individual test and in the small series operation concerning a uniformity of the Gas bubble volumes are obtained, so was now in the feasibility of the Provision of metal foam for mass production of components and parts Composite parts for the vehicle industry found that during a permanent Operate the geometry of the device by melting attack or reaction of Device with a melt can be changed, thereby ensuring stable Gasblasenablösekriterien in continuous operation no longer exists.

As a result, the invention aims at a further embodiment, with which also in continuous operation over long periods stable Gasblasenablösekriterien Foaming a molten metal can be achieved.

The object to provide an embodiment of the device with which also in the Continuous operation over long periods of stable gas bubble removal criteria Foaming a molten metal can be achieved is achieved by that the gas inlet tube at least in the region of the protruding end of a ceramic consists.

The advantages thus achieved are to be seen in particular in that inventive design of the device, the geometry of the same also at long-lasting contact with a hot at least several hundred degrees Celsius Metal melt remains essentially unchanged, which is why even with frequent Use of the device for long periods when foaming Metal melts stable Gasblasenablösekriterien can be achieved. The height Dimensional stability and long service life of the device according to the invention Melt contact makes it possible now, metal foams consistently high Quality in continuous operation without repair or replacement of a device provide. The invention makes use of the knowledge that the ceramic formed parts of the device, optionally the entire device at Comparison with previously used steel-fabricated equipment with molten metal react significantly slower and at the same time with the same geometry the formation of a hydrophobic system with respect to a gas bubble formation in Allow entry of gas into the melt.

A particularly high inertia and thus excellent Performance characteristics are achieved in a device according to the invention, if the ceramic is an oxide ceramic, in particular an aluminum oxide ceramic.

The further object of the invention is a method of the type mentioned specify with which high quality metal foam by blowing gas into it foamable metal can be created is achieved by a uniformity of the Diameter or the size of the individual bubbles and the size of the Gas bubbles through a geometric nozzle design and by adjusting the Influence parameters of the gas are controlled in the molten metal.

The advantages of the metal foam thus obtained are to be seen in particular in that essentially equal bubbles the support criteria of the metallic boundaries under mechanical stress in view of a low specific gravity of the Foam body and a desired material behavior significantly improve.

When metal foam body use oriented with different diameters are each required the same size bubbles, according to the invention to simple Make the uniformity of the size of the individual bubbles by means of the deposition of the Gas inlet tube reaches the melt and the size of the individual bubbles through the Size of the gas outlet cross-section, the size of the entry tube end face and the Height of the gas pressure can be controlled. Own metal foam body respectively equal-volume, but different sized gas bubbles, so is their Material behavior in deformation different, causing certain Applications can be created for a perfectly suitable item.

Extensive experiments have shown that the uniformity of the gas bubble size can be further increased if the gas with an average value oscillating or changing pressure and / or by oscillating moving nozzles in the melt is introduced.

Process engineering, but also with regard to a high product quality can continue from Be advantageous if the gas at a pressure of 0.3 to 12 bar, preferably 0.7 to 5 bar, is blown into the foaming metal.

Particularly lightweight or low density having metal foam body can be created when the metallic melt of light metal, preferably made of aluminum or an aluminum alloy. This can also be a achieved versatile material behavior at low mass of the part become.

The foamability of the metal, but also the formation of the foam matrix or the foam wall can be substantially improved if SiC particles and / or Al ₂ O ₃ particles and other non-metallic particles and / or particles of intermetallic phases are used to prepare the foamable molten metal be used. It is favorable in terms of stability and strength, in particular buckling strength of the foam walls when particles for stabilizing the metal foam with a size of 1 to 50 microns, preferably 3 to 20 microns, used and evenly distributed in the foam matrix, with excellent results can be achieved if in the base metal, a foamable molten metal with a volume fraction of particles of 2 to 50 vol .-%, in particular from 18 to 28 vol .-% is created.

When performing a continuous foaming after the above It has been found that, especially at low particle contents, the Melting to a small extent to bursting above the Melt surface located, come particulate and metal-bearing bubbles can. As a result, bubbles can combine in the flowable metal foam, so that a solidified metal foam larger pores formed from two or more individual bubbles which pores are starting points for material failure mechanical stress, especially at a high punctual Compressive stress, can be.

The aim of the invention to improve the method such that a partial bursting of bubbles is largely prevented, is achieved by the gas at least at a distance S (in millimeters) according to S = - 11.5 + 144.6 x P -0.55 where P is the numerical value of the particle content of the melt in vol .-%, is injected below the melt surface.

The advantages achieved by the development of the invention are, above all, that by providing a riser height according to the invention in the aufzuschäumende molten metal introduced gas bubbles when ascending the Melt surface a minimum path in the particle-containing melt cover must be enough, by whatever route on the surfaces of the gas bubbles Particles can be accumulated to the bubbles as soon as they reach the Have crossed melt surface, to stabilize against bursting. In particular, this also foamable metal melts with low Particle content, for example, of two volume percent, now in a simple way in stable high-quality metal foams are transferred by according to the invention a correspondingly high rise height is provided.

If, as has been found, an oxygen-containing gas, preferably air, In particular, substantially pure oxygen is injected, in Surprisingly, the beneficial effects of a on the particle content of Melt tuned gas bubbles minimum height to be increased because at the Surface of the particle and metal-laden gas bubble at the same time a reinforcing acting oxide layer is formed.

For the provision of starting material for the production of metal foam articles with desired material behavior, the invention also aims to a flowable Metal foam with gas bubbles passing through walls of a liquid metal matrix solid reinforcing particles is limited. This goal is thereby achieved that the diameter of the largest gas bubbles broken by that the smallest gas bubbles gives a value of less than 2.5. Such a flowable Metal foam can be used with high accuracy when using different means Parts are shaped and allowed to solidify, depending on individual bubble size and Ratio of a specific density of the part and its compression behavior at Druckspannungsbeaufschlagung be achieved. Foam parts with a density of each 0.09 to 0.11 experience, for example, only slightly increasing Compressive stresses of 0.25 to 0.8 MPa compression ratios up to 70%.

A metal foam body, which is both high-area and high punctiform mechanical stress withstand, is achieved by that at a Metal foam of the type mentioned the pores substantially spherical and / or ellipsoidal closed, with the largest each Diameter of the pores are distributed monomodally and the pores are essentially made out individual stabilized bubbles are formed and that the wall inner surfaces at least partially coated with an oxide.

A metal foam body according to the invention exhibits an isotropic aspect mechanical properties favorable monomodal size distribution of spatial evenly distributed pores additionally an oxide-reinforced pore wall structure, whereby an increased load capacity achieved in use or a period of use of components with a metal foam unit can be increased. Because of a Formation of the pores such that the pores are substantially single, stabilized bubbles correspond to a flowable metal foam, is suitable Inventive metal foam body for use in components not only at high planar load, but also excellent at high punctiform occurring Burden.

In the following, the invention will be described with reference to only one embodiment illustrative drawings explained in more detail.

Fig. 1 ein Gaseintragsrohr

Fig. 2 ein Gaseintragsrohr mit kegelstumpfförmiger Außenkontur

Fig. 3 einen Düsenstock mit mehreren Gaseintragsrohren

It shows:

Fig. 1 is a gas inlet tube

Fig. 2 is a gas inlet tube with frusto-conical outer contour

Fig. 3 shows a nozzle with several gas inlet tubes

In Fig. 1, a gas inlet tube 1 is shown, which with an extent E in a Melt protrudes. The gas inlet tube 1 has between inner surface 4 and outer surface 5 a constant wall thickness with a pipe end face 3, the into the melt S sticks up.

2 shows a gas introduction tube 1 with a Einragemaß E in a melt S, which tube 1 in the exit region a frustoconical or truncated pyramidal Outer contour 6, which in the extension at an angle to the axis 7 of a Gas inlet channel has. With such an embodiment of a Gas inlet tube 1 can with high stability and strength of the base part a Pipe end face 3 formed with the smallest surface area up to a front edge become.

From Fig. 3 is an embodiment with a nozzle 8, which is preferably arranged detachably in a wall 9 of a melt vessel, removable. Three gas inlet tubes 1, 1 ', 1 "projecting into a melt S are arranged at a distance A ₁ and A _{2 from} each other in the nozzle 8. Such easily exchangeable nozzle rods 8 are preferably used when metal foams having substantially the same single bubble volume but different Produce bubble sizes, because thereby the formation criteria: size of the gas outlet cross-section and size of the gas inlet tube end face, can be changed in the short term.

Based on the schematic drawings, the bubble forming mechanisms again briefly stated:

If an introduction of gas into a melt S, so in this at the Outlet opening 2 of the entry hole 1 a convex concavity formed. Around enlarging curvature hangs the melt on the surrounding surface of the Gas outlet. Because now the interface system melt / wall than hydrophobic system is the adhesion of the liquid metal around the Gas outlet opening low, resulting in separation phenomena and flat emigration the gas bubble boundary leads to the wall. Thereby are the Separation conditions for the gas bubble largely indefinite, leading to can lead to a variety of bubble sizes. Should by means of several adjacent Outlet bubbles are created so they unite in most Falls, whereby a desired foaming is prevented or a Uneven bubble structure of the metal foam is formed.

Now, for example, has a gas inlet tube 1 projecting according to the invention a Inner diameter D2 and a gas outlet cross-section 2 and a Outside diameter D1, the result of the measure of the pipe end surface. 3

When gas is introduced into the melt, however, the gas bubble limitation can only emigrate to the outer edge of the pipe end face 3, whereby an essential Influence on the separation criteria is given. Also adjacent gas inlet tubes 1, 1 ', 1 ", which protrude into a foamable melt S, form on the basis of the Outside edges of the end surfaces 3 recessed surfaces defined separation criteria for Gas bubbles out, allowing a union and formation of large bubbles largely is excluded.

Fig. 4: die Abhängigkeit der erfindungsgemäß vorgesehenen Mindeststeighöhe vom Partikelgehalt der Schmelze.

Fig. 5: die Porengrößenverteilung eines erfindungsgemäßen Metallschaumkörpers.

In the following, an embodiment of the invention with reference to figures is explained in more detail by way of example. show:

4: the dependence of the inventively provided Mindeststeighöhe the particle content of the melt.

5 shows the pore size distribution of a metal foam body according to the invention.

In extensive series of experiments different particle-containing Aluminum alloys, for example AlSi7Mg, also known as A 356 Aluminum alloy with, in addition to aluminum, essentially 7 wt .-% silicon and 1 Wt .-% magnesium, or for example AA 6061 (aluminum alloy with a Composition according to standard Aluminum Association number 6061), in one Melting crucible melted, with an adjustment of the particle content in the Melting optionally by mixing one in the chemical Composition corresponding paritikelfreien alloy took place. Subsequently Gas was introduced into the particle-containing melts. The entry was made in all Try each of a single nozzle body with an outlet opening, wherein Nozzle bodies made of chrome-nickel steel and ceramic were used.

In a first series of experiments, the durability of various nozzle bodies was investigated. When performing five Aufschäumversuchen over periods of 20 seconds up to 45 minutes with chromium-nickel steel nozzles on the one hand and with aluminum oxide nozzles on the other hand, the steel nozzle, which were more than about 2 minutes in use, visually changed the shape of the gas outlet opening Melting attack can be determined. Correspondingly, the metal foam created at the beginning and at the end of the foaming process and removed from the melt surface had different pore diameters. In contrast, with the alumina nozzle bodies, even such continuous changes over 45 minutes did not reveal any such geometry changes. Accordingly, metal foam with equivalent pore properties could be produced throughout the experimental period. Other ceramic materials, such as SiO ₂ or SiO ₂ / Al ₂ O ₃ , can be used with advantage over steels; maximum service life is achieved comparatively but with nozzle bodies made of Al ₂ O ₃ .

In a second series of experiments, the height of rise S of the introduced gas was varied with nozzle bodies made of alumina at a fixed particle content P of the melt, and the quality of the metal foams formed at different gas injection depths was investigated. The following behavior was shown with reference to FIG. 4: With a low particle content P of the melt, for example 2% by volume, metal foam can be formed at a low rise height S, in which, in the case of a cross-sectional view, pores are present which consist of at least two bubbles are formed. Such pores are easily recognizable by being ellipsoidally elongate with a high ratio of the longer to the shorter axis. Such a behavior can be found in the examined particle contents in the riser height region A of FIG. 4. However, as soon as the rise height S at a given particle content P no longer comes to lie in the region A of FIG. 4, but is increased such that it falls in region B, a metal foam can be created in which the bubbles due to the increased climbing path enough parcels on the surface can be collected to be stabilized against bursting in the liquid metal foam. The experimentally determined necessary heights for substantially complete bubble stabilization are plotted in FIG. 4 for various particle contents in the form of triangles. The line separating region A and region B represents a compensation curve of the general form adapted to the experimental data Y = a + X b represents.

In compliance with the minimum height of height were in the metal foam in cross section to more than 95%, sometimes more than 99%, pores found to be individual Gas bubbles corresponded. Fig. 2 shows the pore size distribution of a Metal foam, in compliance with the Aufschäumbedingungen invention was created. As can be seen by the histogram in Fig. 5, is at a monomodal distribution of pore sizes at a mean value of 4 mm Proportion of pores of about 6 mm proportionately only slightly higher than that of 2 mm, that is, the pore sizes are approximate to both sides of an average distributed to the same extent or the same frequency.

In a third series of experiments, the effects of the injected gas became apparent studied the material composition and the material properties. It has become in the context of secondary electron microscopic (SEM) investigations unexpectedly demonstrated that when using oxygen-containing gases, such as less expensive air, at the pore surfaces in subregions an additional layer of an oxide is trained. The oxide layer acts on the metal foam reinforcing, like a 5 to 7% increase in the compression of metal foam bodies according to the invention on half volume showed necessary deformation energy. A further increased Increase in the same deformation energy of about 10% was at the Use of pure oxygen observed as a foaming gas. In that case, as could be shown by means of SEM images, the wall inner surfaces in the Essentially complete, d. H. at least 90%, coated with an oxide layer.

Claims (20)

Device for introducing gas into a melt of foamable metal by means of at least one tube for the production of metal foam, characterized in that the gas inlet tube (1) projecting into the melt (S) protrudes and at the projecting end a gas outlet cross section (2) with an area of 0.006 to 0.2 mm ² and a pipe end face (3) of less than 4.0 mm ² has. Apparatus according to claim 1, characterized in that the outlet opening (2) of the gas introduction tube (1) to an extent (E) of at least 5 times, preferably at least 10 times, the value of the largest inner dimension (D2) of the outlet opening (2) is formed protruding into the melt. Apparatus according to claim 1 or 2, characterized in that the gas inlet pipe (1) has a circular gas outlet opening (2) and a pipe end edge or annular pipe end face (3). Device according to one of claims 1 to 3, characterized in that in the melt (S) einragende gas introduction tube (1) at least in the region of the gas outlet end (2) has a spherical segment, truncated cone or truncated pyramid outer contour (6). Device according to one of claims 1 to 4, characterized in that the angle (α), which includes the generatrix (61) of the stump surface (6) with the axis (7) of the gas inlet channel, a value of less than 60 °, preferably from less than 45 °. Device according to one of claims 1 to 5, characterized in that at least 2, preferably more than 2 Gaseintragsrohre (1,1 ', 1 "), in particular with the same mutual distance (A1, A2), which is preferably greater than having 10 times the Einrageausmaßes (E) of the outlet opening in the melt, are arranged in a replaceable nozzle (8) in the melt vessel (9) of metal foam plants. A ≥ 10 x E Device for introducing gas into a melt of foamable metal by means of at least one tube for producing metal foam, wherein the gas inlet protrudes projecting into the melt and at the projecting end a gas outlet cross-section with an area of 0.006 to 0.2 mm ² and a tube end face of smaller 4.0 mm ² , characterized in that the gas inlet tube consists of a ceramic at least in the region of the projecting end. Apparatus according to claim 7, characterized in that the ceramic is an oxide ceramic, in particular an aluminum oxide ceramic. A method for producing metal foam by injecting gas into a foamable molten metal, characterized in that a uniformity of the diameter or the size of the individual bubbles and the size of the gas bubbles are controlled by a geometric nozzle design and an adjustment of the Einströmparameter the gas into the molten metal , A method according to claim 9, characterized in that the uniformity of the size of the individual bubbles achieved by means of the deposition of the gas introduction tube into the melt and the size of the individual bubbles are controlled by the size of the gas outlet cross-section, the size of the entry tube end face and the height of the gas pressure. A method according to claim 9 or 10, characterized in that the gas is introduced with an oscillating by an average value or changing pressure and / or by oscillating moving nozzles in the melt. Method according to one of claims 9 or 10, characterized in that the gas at a pressure of 0.3 to 12 bar, preferably at 0.7 to 5 bar, is blown. Method according to one of claims 9 to 12, characterized in that the metallic melt of light metal, preferably made of aluminum or an aluminum alloy is created. Method according to one of claims 9 to 13, characterized in that for the preparation of the foamable molten metal SiC particles and / or Al ₂ O ₃ particles and other non-metallic particles and / or intermetallic phase are used. Method according to one of claims 9 to 14, characterized in that particles for stabilizing the metal foam with a size of 1 to 50 microns, preferably 3 to 20 microns, are used. Method according to one of claims 9 to 15, characterized in that the foamable molten metal with a volume fraction of particles of 2 to 50 vol .-%, preferably 18 to 28 vol .-%, created. Method according to one of claims 9 to 16 for producing metal foam by blowing gas into a foamable molten metal, wherein a uniformity of the diameter or the size of the respective individual bubbles and the size of the gas bubbles are controlled, characterized in that the gas in at least one Distance S (in millimeters) according to S = -11.5 + 144.6 x P -0.55 where P is the numerical value of the particle content of the melt in vol .-%, is injected below the melt surface. Method according to one of claims 1 to 17, characterized in that an oxygen-containing gas, preferably air, in particular substantially pure oxygen, is blown. Flowable metal foam with gas bubbles, which are bounded by walls of a liquid metal matrix with solid reinforcing particles, characterized in that the diameter of the largest gas bubbles broken by that of the smallest gas bubbles results in a value of less than 2.5. Metal foam body with spatially evenly distributed, enclosed by a solid wall pores, wherein the wall consists of a metallic matrix and embedded in these particles, characterized in that the pores are formed substantially spherical and / or ellipsoidal closed, wherein the respective largest diameter of Pores are monomodally distributed and the pores are formed essentially of individual stalized bubbles and that the inner wall surfaces are at least partially coated with an oxide.

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