EP1036615B1 - Process for foaming metallic articles - Google Patents

Abstract

Semi-finished product foaming involves heating in a chamber using external radiation. A semi-finished product, consisting of metal powder and blowing agent powder and optionally joined to one or more cover layers, is foamed in a chamber by heating with external radiation. An Independent claim is also included for apparatus for carrying out the above process, comprising a chamber (10) with radiation transparent or translucent walls (20, 22, 24) and a chemically inert, radiation transparent or translucent protective layer (26, 28) enclosing the semi-finished product (12) to be foamed.

Description

The invention relates to a method for foaming one of at least a metal powder and at least one gas-releasing propellant powder existing Pressings, which is optionally connected to at least one cover layer, wherein the Pressling is placed in a room and heated to foaming. Further The invention relates to the use of a device for foaming a Compact.

From DE 44 26 627 C2 discloses a method and an apparatus for the production of metallic Composite materials of one or more cover layers of solid material and from a core located between them, known by compression a mixture of at least one metal powder and at least one gas-releasing Propellant powder is formed. A composite thus formed is then placed in a chamber furnace introduced at a temperature of 850 ° C. At this temperature foams the Pressling to the extent necessary without melting the outer layers.

The heating is thus carried out by heat transfer such that initially over indirectly transfer the heat to the pellet via a foaming tool becomes. Such a method is energetically unfavorable and often leads to overheating of the foam, so that the composites produced are not the required Have goodness. Furthermore, it is hardly possible to initiate targeted heat in the semifinished product in such a way that reproducible areas of the compact are foamed differently.

From DE 197 34 394 A1 an apparatus and a method for the production of Metal foam known. In this case, material to be foamed in a foaming cell heated, which leaves the foaming cell via an outlet opening, while before, during or foams after exiting. Heating can be done by induction heating respectively.

DE 44 13 423 A1 relates to a device for the digestion of substances. A substance to be analyzed can be placed in a quartz glass vessel be introduced, the substance side with a protective layer z. B. made of boron nitride is.

The present invention is based on the problem with high efficiency and energetic low-foaming compacts, with the additional possibility to be given is intended to heat different areas of the compact different or, where appropriate to observe the foaming in order to be able to intervene in a targeted manner.

According to the invention, the problem is essentially solved by the fact that the compact is foamed by externally injected into the room radiation energy, wherein the space of a transparent, semitransparent or translucent wall is limited, at least the space inside with one opposite the foamable compact and the optional topcoat chemically inert, permeable to the coupled radiation energy or substantially permeable protective layer is provided. Notwithstanding the previously known In the prior art, there is no heat transfer from the billet receiving Space itself, but energy coupled into the space from outside. This is it in particular radiation energy in the middle or far infrared range. Also Radiation in the microwave range comes into question.

As a wall of the space receiving the compact, applied to the protective layer In particular quartz glass material or such containing is in question.

The use of a semi-transparent material has the advantage that the foamable Material not by the otherwise acting as a cold pole wall "shocked" is.

Al ₂ O ₃ and / or Si ₃ N ₄ and / or BN and / or SiO ₂ / Al ₂ O ₃ and / or mixtures thereof may be used as the protective layer. In this case, the protective layer can be applied to the inner surfaces of the wall, optionally via a bonding agent layer, by PVD methods. In particular, electron beam evaporation, magnetron sputtering, cathodic arc evaporation or plasma immersion ion implantation come into question.

In particular, it is provided that the protective layer such as aluminum oxide layer is coupled via at least one graded intermediate layer in particular of silicon and aluminum oxide to the wall as the quartz glass component, in particular the protective layer such as aluminum oxide layer by physical vapor deposition and / or chemical vapor deposition is deposited and preferably the alumina is formed by post-oxidation of an aluminum layer by means of plasma treatment and / or thermal oxidation or reaction with SiO ₂ .

Furthermore, the invention relates to the use of a device with one of a wall limited space and a radiant energy einkoppelnden in the room Energy source, wherein the wall opposite to the input radiation energy is transparent or at least translucent and at least room inside with a chemically inert to the foamable material and to the radiant energy transparent or translucent protective layer is covered, for foaming a arranged in the space consisting of at least one metal powder and at least one gas-releasing propellant powder consisting of existing compact.

The thickness D of the wall itself should be in the range between 5 and 25 mm in particular about 15 mm.

The heat source itself is preferably IR emitters, the Radiation energy is coupled in such a way that in the foaming body Heat sinks can form. This allows a targeted foaming geometry and targeted density gradient can be achieved.

With respect to the protective layer, which may be mentioned as being Al ₂ O ₃ or Si ₃ N ₄ or BN material or containing it, it should be noted that the thickness thereof should be in the range between 20 nm and 2 μm.

By the teachings of the invention is a structurally simple design a radiant heat into the frothy body or body einkoppelbar, wherein compared to conventional methods, where a heat transfer by means of Heat emitted by the furnace walls takes place, a considerable energy saving and in particular a time gain of up to 50% results. Overheating of the foam is excluded. Also, no reheating takes place, whereby the cycle times of the foaming otherwise would be adversely affected.

Due to the einkoppelbare radiation energy also gives the advantage that areas the foaming semi-finished can be subjected to targeted heat, so that mentioned already by the foaming a desired geometry education can be done.

By the use of quartz glass material to form the walls, the Surrounded by frothing to press, arrive mechanically durable long-term stable Materials are used that are manufactured and used inexpensively can. Here, the quartz glass ensures that heat radiation, especially in the Infrared range up to 2 microns and in the range between 3 and 3.5 microns with a transmission coefficient between 0.8 and 0.9 can be coupled. Furthermore, results in the Use of quartz glass the possibility of visual observation during foaming, so that a controlling intervention during foaming is possible.

Preferably, the wall can consist of quartz glass components. Quartz glass is because of its high melting point and high transparency in the infrared and in the visible spectral range for coupling heat radiation into hot, liquid and gaseous media and for the observation of the processes themselves suitable. When contact However, reactions occur with chemically aggressive media such as liquid aluminum on, the quartz glass parts or components made therefrom within a short time to destroy.

For molds, reaction vessels or pipelines that come into contact with liquid aluminum, various ceramics such. B. Si ₃ N _{4 is used} in the form of sintered components. However, corresponding materials are neither transparent in the infrared nor in the visible spectral range, so that the materials themselves are heated by heat conduction alone. A visual observation of processes even within corresponding devices is also not possible.

To use quartz glass for this, without the risk of unwanted arises chemical reaction with aggressive media, the invention proposes that the transparent glass block on its facing the material Side chemically passivated and provided with a protective layer of aluminum oxide. This may have a thickness between 20 nm and 2 microns. In particular provided that the alumina layer is made up of a graded interlayer Silicon and / or alumina is coupled to the base material.

According to a development of the invention it is provided that the particular from Quartz glass moldings modular design in a carrier mount to the radiation source is transported away or from this, whereby a charging or a Handling the foamable or foamed materials is facilitated.

Further details, advantages and features of the invention not only result from the claims, the characteristics to be taken from them-alone and / or in combination- but also from the following description of one of the drawings taking preferred embodiment.

Fig. 1

eine Vorrichtung zum Herstellen eines aufschäumbaren metallischen Werkstoffes und

Fig. 2

eine beschichtete Quarzglasplatte.

Show it:

Fig. 1

an apparatus for producing a foamable metallic material and

Fig. 2

a coated quartz glass plate.

In Fig. 1, a device 10 is shown, in which a compact 12, on opposite Provided with metal cover layers 14, 16, foamed to a metallic composite of light weight, However, to produce high strength. Appropriate composites form efficient Lightweight structures, the z. B. in traffic engineering used. Such composites are characterized by low density at relatively high Stiffness out.

The compact 12 may consist of a mixture of aluminum powder and z. B. 12% by weight Silicon powder and 0.8% by weight of titanium hydride powder as gas-releasing Propellant powder be composed, which then mixed precompacted into a billet become. This can be open or closed pore. Then the compact 12 has been covered with the cover layers 14, 16 by rollers. If the compact 12 was open-pored, this step becomes a necessary closed porosity achieved. The temperature during rolling itself is about 400 ° C.

The sandwich body thus formed is then introduced into a space 18, which a wall 20 is limited, which consists of quartz glass material. In the embodiment the space of a cup-shaped lower part 22 and this final Cover part 24 is formed. Inside the room are the walls with a Protective layer 26, 28 provided, the radiation to be coupled into the space 18 is permeable. The thickness of the wall 20 itself is also chosen so that this is transparent or translucent with respect to a radiation that can be coupled in.

The receptacle is circumferentially surrounded in the embodiment of infrared radiators, exemplified by reference numerals 30, 32.

The protective layer 26 is preferably one of Al ₂ O ₃ , Si ₃ N ₄ , BN or SiO ₂ / Al ₂ O ₃ or containing these materials. The protective layer is compared to the aggressive material of the compact, so in particular when using aluminum powder against this chemically inert, so that the otherwise vulnerable to aluminum quartz material is protected. The thickness of the protective layer 26, 28, however, is selected such that it is also transparent or translucent with respect to the radiation to be coupled in. Thus, radiation can be coupled in from the outside into the space 18 to the extent necessary to heat the compact 12 to a temperature that allows foaming. The infrared radiators 30, 32 can be arranged around the space 18 in such a way that heat sinks can form in the pressed body 12, whereby targeted geometry formation and / or density gradients can be achieved during foaming.

The space 18 may further have an internal geometry, that of the final geometry should correspond to the foamed workpiece. For a simple geometry adjustment to allow the walls 20 can be modular, so that with simple measures a change is possible.

The protective layers 26, 28 are preferably by PVD method, in particular by electron beam evaporation, magnetron sputtering, arc evaporation or Plasma immersion ion implantation applied.

So that the protective layer 26, 28 sufficiently protects the quartz glass material, its Thickness between 5 and 25 nm, in particular in the range of 10 nm. The wall itself has a thickness D of 15 mm.

The emitters 30, 32 preferably emit light in the mid-infrared range. Regardless, however, the wavelength should be based on the material of the wall and the Be matched protective layer to ensure a high degree of transmission.

In Fig. 2 is purely in principle a z. B. for a Kokillenanordnung particular bottom plate 34 made of quartz glass, the z. B. dimensions of 180x80x5 mm ³ has. The plate 34 has on its kokilleninnenseitiger surface 36 in an approximately 1 micron thick and adherent layer 38 of Al ₂ O ₃ . As a coating method, the electron beam evaporation of an Al ₂ O ₃ melt can be used. The coating is carried out at a residual gas pressure of about 1 x 10 ^-4 mbar.

The corresponding plate 34 may be in a mold, not shown, with the layer 38 be used facing the interior. Both when pouring liquid aluminum as well as the melting of an aluminum sheet by means of infrared radiation, the was coupled through the transparent plate 36, a reaction with the Quartz glass plate 34 liquid aluminum can not be determined. After cooling could a solidified aluminum part without difficulty from the coated quartz glass plate 34 are removed.

The mold itself may be arranged in a carrier receptacle for transport to facilitate a heat source such as infrared radiators or away from them. hereby There is a simplification of the charging or the handling of the foaming or foamed materials.

Claims (12)

1. A method for foaming of a pressed part comprising at least one metal powder and at least one gas-separating propellant powder and if necessary connected to at least one cover layer, where said pressed part is arranged inside a space and heated in order to foam it,
   wherein
   the pressed part is foamed by a radiation energy injected from the outside into the space, the latter being limited by a transparent, semi-transparent or translucent wall which is at least on the inside of the space provided with a protective layer chemically inert to the foamable pressed part and permeable or substantially permeable for the injected radiation energy.
2. Method according to Claim 1,
   wherein
   a protective layer is used that is chemically inert to the cover layer where provided.
3. Method according to at least Claim 1 or Claim 2,
   wherein
   the pressed part is heated with a radiation of a wavelength λ at 700 nm < λ < 4 µm, in particular at 3.0 < λ < 3.5 µm, or with a mid infrared radiation or with a far infrared radiation or with a radiation in the microwave range.
4. Method according to at least one of the previous claims,
   wherein
   transparent or semi-transparent shaped material such as quartz glass material or containing such material is used as the wall of the space receiving the pressed part relative to the radiation to be injected.
5. Method according to at least one of the previous claims,
   wherein
   Al₂O₃ and/or Si₃N₄ and/or Al₂O₃/SiO₂ and/or BN or material containing the latter is used as the protective layer, where said protective layer is preferably provided with a thickness d of 8 nm ≤ d ≤ 2 µm, in particular d approximately 20 nm to 500 nm.
6. Method according to at least one of the previous claims,
   wherein
   the protective layer is deposited by PVD process, by electron beam evaporation, magnetron sputtering, arc evaporation or plasma immersion ion implantation.
7. Method according to at least one of the previous claims,
   wherein
   the radiation energy is injected such that heat sinks are formed in the pressed part.
8. Method according to at least one of the previous claims,
   wherein
   the protective layer such as aluminium oxide layer (38) is connected via at least a graduated intermediate layer, in particular of silicon and aluminium oxide, to the wall such as the quartz glass component (34), wherein in particular the protective layer such as the aluminium oxide layer is deposited by physical deposition from the vapour phase and/or by chemical deposition from the gas phase, and wherein the aluminium oxide is preferably formed by post-oxidation of an aluminium layer by means of plasma treatment and/or thermal oxidation or reaction with SiO₂.
9. Use of a device with a space limited by a wall and of an energy source injecting radiation energy into said space, where the wall is transparent or at least translucent to the injectable radiation energy and is covered at least on the inside of the space with a protective layer chemically inert to the foamable material and transparent or at least translucent to the radiation energy, for foaming of a pressed part arranged inside the space and comprising at least one metal powder and at least one gas-separating propellant powder.
10. Use of a device according to Claim 9, where the wall is designed on a quartz glass basis, in particular in the form of quartz glass modules, where the wall is designed modular if necessary, and where the wall preferably has a thickness D of 5 mm ≤ D ≤ 25 mm, in particular with D approximately 15 min.
11. Use of a device according to Claim 9, where the protective layer comprises Al₂O₃ and/or SiO₂/Al₂O₃ and/or Si₃N₄ and/or BN or material containing the latter and preferably has a thickness d of 20 nm ≤ d ≤ 2 µm.
12. Use of a device according to one of Claims 9 to 11, where the heat source is in particular at least one IR heater and where the heat source is preferably arranged outside the space such that heat sinks can form indcside the pressed part.

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