Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Reexamination Certificate
2000-02-02
2001-07-03
Jenkins, Daniel (Department: 1742)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
C428S049000, C428S068000, C419S002000, C419S036000, C419S037000, C419S054000, C264S610000, C264S628000, C264S640000, C264S666000
Reexamination Certificate
active
06254998
ABSTRACT:
The present invention relates to novel methods for producing cellular structures, referred to as foam structures, and to foam structures produced by such methods that are suitable for uses as absorbers of mechanical energy as, for example, in automobile components, and also as light weight structural elements in support systems, etc.,
BACKGROUND OF THE INVENTION
There are a large variety of methods for producing metal and ceramic foams or similar porous metal structures starting from liquid or powdered metals [1]. Currently there are two ways for directly foaming metals. The first of them involves melting the Al matrix metal, adding reinforcing particles to the melt (5-20% SiC or Al
2
O
3
) and injecting gas (air, nitrogen, argon) into the melt using a rotating impeller. The second technique for directly foaming melts is to add a foaming agent to the melt. The foaming agent decomposes under the influence of heat and releases gas, which then propels the foaming process [1-3]. Another method, which was developed some years ago in the Ukraine, exploits the fact that some liquid metals form a eutectic system with hydrogen gas. As the melt cools bubbles of hydrogen are released [4, 5].
Metal and ceramic foams can also be fabricated using open porosity polymer foams as a starting point. The polymer foam is filled with a slurry of heat resistant material, e.g. a mixture of mullite, phenolic resin and calcium carbonate. After drying the polymer is removed and molten metal is cast into resulting open voids. After removal of the mold material (e.g. by water under high pressure) metallic foam is obtained, which is an exact image of the original polymer foam [1]. Polymer foams can also be used in a deposition technique. Metal is deposited on the polymer foam, then the polymer is removed by heating.
Another method for foam calls for casting around inorganic granules of hollow spheres of low density or by infiltrating such materials with a liquid melt [6]. Powder metallurgy methods [1, 7-8] include mixing powders with a foaming agent, compaction of the powder blend into a dense precursor material and foaming of the precursor material by heating it to its melting temperature. Foams can also be produced by preparing a slurry of metal or ceramic powder mixed with a foaming agent. The slurry becomes more viscous and starts to foam during drying in a mould at elevated temperature [1, 9-10].
Most foaming techniques work well for lightweight low-temperature metals, predominantly aluminum and its alloys, but can not be used for fabrication of high-temperature metallic or ceramic foam. However, there is a need for a universal method, which could be applied to the fabrication of foams from any material—metals, ceramics, intermetallics, composites. The vast majority of existing techniques do not allow rigid control of cell shape and size. Thus there arises a wide variation of cell sizes, an uneven distribution of cells in the foam volume and, as a result, a wide scatter in mechanical characteristics.
REFERENCES
1. J. Banhart, “Production Methods for Metallic Foams”, Metal Foams/Fraunhofer USA Symposium “Metal Foam”, Stanton, Delaware, Oct. 7-8, 1997.Ed.: J. Banhart and H. Eifert.—Bremen: MIT-Verl., 1998, pp.3-11
2. J. Banhart, P. Weigand, “Powder Metallurgical Process for the Production of Metallic Foams”, Metal Foams/Fraunhofer USA Symposium “Metal Foam”, Stanton, Del., Oct. 7-8, 1997.Ed.: J. Banhart and H. Eifert.—Bremen: MIT-Verl., 1998, pp.13-22
3. J. Wood, “Production and Applications of Continuously Cast, Foamed Aluminum” Metal Foams/Fraunhofer USA Symposium “Metal Foam”, Stanton, Del., Oct. 7-8, 1997.Ed.: J. Banhart and H. Eifert.—Bremen: MIT-Verl., 1998, pp.31-36
4. A. Pattnaik, S. C. Sanday, C. L. Vold, and H. I. Aaronson, “Microstructure of Gasar Porous Ingot”,
Materials Research Society Symposium Proceedings, Vol.
371,
Advance in Porous Materials
, December 1994, p. 371-376T.
5. J. M. Wolla and V. Provenzano, “Mechanical Properties of Gasar Porous Copper”,
Materials Research Society Symposium Proceedings, Vol.
371,
Advances in Porous Materials
, December 1994, p. 377-382.
6. W. Thiele, German Patent, 1933321, 1971
7. J. Baumeister, U.S. Pat. No. 5,151,246, 1992, German Patent 4018360, 1990
8. J. Baumeister, J. Banhart, M. Weber, German Patent DE 4401630, 1997
9. J. Drolet, Int. J. Powder Met., 13, 223, 1977
10. S. Kulkarni, P. Ramakrishnan, Int. J. Powder Met., 9, 41, 1973
OBJECTS AND ADVANTAGES OF THE INVENTION
It is an object of the present invention to provide a novel method using powdered materials for producing foam structures comprised of materials such as ceramics, metals, intermetallics and polymers.
It is a further object to provide such method to produce foam structures suitable for making structures usable as light weight, structural components, filters, catalyst carriers, heat exchangers, etc.
The methods of the present invention enable the production of novel foam structures with cells of predetermined and controllable size and distribution.
The methods of the present invention for making foam allow control of the final porosity (from a few volume percent to more than 95 vol. % and more), cell size and interchannel wall thickness (from a few microns to a few millimeters) with small tolerance.
An object of the present invention is to demonstrate a novel low cost near-net-shape fabrication technology, which allows precise control of cell size and distribution in the metal and ceramic foams and makes possible a mass production of such foam structures.
SUMMARY OF THE INVENTION
In accordance with the present invention, a foam structure comprising a body of structural material having a plurality of cells therein is produced by forming a composite rod comprising an outer shell formed of a powdered form of the structural material and a binder material and an inner core formed of a powdered form of a removable channel forming filler material and a binder material. The composite rod is sectioned into a plurality of rod segments of predetermined length and a plurality of these segments are assembled in randomly oriented relationship to one another. The assembly of rod segments is then consolidated. The binder and the filler core material are then removed and the resulting structure is sintered to produce the final foam structure containing cells as defined by the removed filler material. The binder and filler core material may be removed before sintering, during the sintering process or after sintering. Such removal will depend upon the specific binder and filler materials that are used, and such removal may be accomplished by evaporation, decomposition, dissolution, infiltration, melting with following blow out, etc.
In one embodiment, the structural material is a sinterable ceramic powder, such as alumina; the channel forming filler of the core is melamine or urea or a polymer, such as polyethylene or polypropylene; and the binder of both the core and outer shell is paraffin or wax.
Preferably, the viscosity or yield points of shell and core mixtures at extrusion temperature should be as close as possible to one another.
In the preferred embodiment, the binder is removed by heating. The filler core material can also be removed by heating, and this can be accomplished during the application of the heat used to preform the sintering step, which will require higher temperature than the melting or boiling point of the filler material.
In another preferred embodiment, the structural material of the shell is formed of a powdered ferrous metal, such as iron or steel, and the channel forming filler material of the core is an organic powder, such as melamine. In this embodiment, the binder has a lower melting point than the core filler and may be paraffin or bees wax.
In a further embodiment, the consolidated assemblage of segments is placed between two plates, formed of metal powders, preferably iron, and a binder, and the sandwich of the two plates and consolidated assemblage is then die compressed and heated to an el
Jenkins Daniel
Materials and Electrochemical Research (MER) Corporation
Teplitz Jerome M.
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