Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2002-10-09
2004-12-07
Jones, Deborah (Department: 1771)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S403000, C428S407000, C428S469000, C428S701000
Reexamination Certificate
active
06828026
ABSTRACT:
This is a nationalization of PCT/DE01/00349 filed Jan. 24, 2001 and published in German.
The invention relates to hollow balls having shells comprising a sintered inorganic material, such as metals, metal oxides or ceramics, and to methods for producing the hollow balls of lightweight structural components using such hollow balls.
EP 0 300 543 A1 and U.S. Pat. No. 4,917,857 have described a method for producing metallic and ceramic hollow balls. In this case, an aqueous suspension of a metallic or ceramic powder with an organic binder is applied to a ball-shaped core of a foamed polymer, and the polymer which forms the core is pyrolyzed during a heat treatment (400 to 500° C.), during which treatment the gaseous components escape and what is referred to as a green body of sufficient stability is obtained.
This green body is then heated further, in order also to expel the organic constituents of the binder which have hitherto remained in place and to sinter the powder particles together to form a closed ball shell.
Furthermore, DE 197 50 042 C2 has described in particular the application of the pulverulent starting material together with a liquid binder to a core by using a rotor to roll it around.
The hollow balls with a shell which are obtained in this way and substantially comprise the powder material can be used for various applications.
One such application is described in DE 198 17 959 C1 for lightweight structural components. According to this document, such hollow balls, which are known per se, are to be mixed with a polymer adhesive to form a “slurry of balls”, and this “slurry of balls” is to be introduced into a mold or between two surface plates before the adhesive is cured. A certain limited time window in which the suitably pretreated balls have to be processed is available for this purpose before the adhesive cures.
Moreover, when mold bodies with difficult geometries, for example those with undercuts, are being filled, there are problems with completely filling the entire volume of the mold body with a “slurry of balls” of this type.
After the adhesive (polyurethane or polyester based, an epoxy adhesive or PMMA) has cured, the adhesive forms a solid bond for the hollow balls forming a lightweight structural component of this type, but on the one hand this is not always completely successful on account of the possibility of segregation and on the other hand for some applications this is also undesirable.
However, if the hollow balls are introduced into a mold body first and then the more or less viscous adhesive is introduced, it is impossible to achieve a homogenous distribution of adhesive in the mold body.
Therefore, it is an object of the invention to improve hollow balls having shells of sintered inorganic material in such a way that their range of application is widened, processing to form structural components is technologically simplified and the properties of the hollow balls and of the structural components produced therewith are improved for specific applications.
The hollow balls according to the invention are based on conventional solutions but have at least one additional functional layer on the spherical shell, which consists of a sintered, at least predominantly inorganic material. The functional-layer material, components contained therein or components which are applied to a functional layer can be made able to flow, plastically and/or elastically deformed by means of a physical and/or chemical treatment. As a result, the shells and consequently also adjacent hollow balls can be fixed to one another in an adhesive and/or positively-locking manner.
The shells may consist of metal, a metal alloy, a metal oxide or a ceramic. They may be as far as possible free of organic constituents. Examples of suitable metals are iron, nickel, copper and light metal, e.g. titanium, aluminum or high-melting heavy metals, such as for example tungsten or molybdenum and alloys thereof.
The physical and/or chemical treatment and the selection of materials should preferably be such that at least the shells of the hollow balls do not become unstable during the treatment.
It is also possible for a plurality of functional layers to be formed above one another in the manner of an onion skin, in which case the corresponding choice of materials may cover various applications. In this case, the treatment of such hollow balls may also be carried out in a plurality of steps specific to the particular application.
A hollow ball according to the invention with an additional solid functional layer which has been additionally applied, for example by application of a suspension to the shell, and dried or cured, represents an initial product which can be processed better and more easily than the conventional hollow balls, and these hollow balls save the final manufacturer of structural components a number of technological process steps.
It is possible to use hollow balls without a functional layer with an external diameter of 0.1 to 20 mm, preferably 0.5 to 5 mm. In this case, the shell may have a thickness which corresponds to 0.1 to 50%, preferably up to 10%, of the external diameter of the hollow balls.
The functional layer(s) according to the invention should have a thickness which, after the physical and/or chemical treatment of the hollow balls, ensures the appropriate functional effect, for example protection against corrosion or an adhesive bond between adjacent hollow balls. However, the thickness should advantageously be selected to be at least sufficiently great for it to be possible to achieve positively locking fixing of adjacent hollow balls during the plastic and/or elastic deformation.
It is generally sufficient for the thickness of a functional layer to be less than the thickness of the shell. The thickness of a functional layer should be no greater than 0.9 times, preferably 0.1 times to 0.5 times, the thickness of the shell of the corresponding hollow ball. This allows functions, such as for example the joining of adjacent hollow balls to form a lightweight structural component, protection against corrosion for the metal shells, electrical and magnetic properties, to be achieved.
Moreover, the mass of at least one functional layer or a plurality of these layers should not exceed the mass of the shell.
For positively locking fixing of adjacent hollow balls by means of the functional-layer material, it may be sufficient for at most 80% of the surface of the shell to be covered.
This allows the mass of a lightweight structural component produced from hollow balls to be reduced.
The hollow balls according to the invention should be able to flow freely and should not stick to one another, so that they can be processed without problems after storage and transport.
An additional sealing layer may be applied to the functional layer, in particular to provide temporary protection during transport and storage, so as to form very smooth, non-adhesive surfaces. By way of example, quick-drying, preferably water-soluble coatings or other more or less viscous liquids can be sprayed on. Suitable examples are cellulose or pectin solutions or polyvinyl alcohol.
The functional layers may be formed from a homogenous material but may also be formed from composites.
For example, for certain applications (e.g. for detection purposes), ferromagnetic and/or permanent-magnet particles may be embedded in the functional layer.
However, the functional layer may also be doped or formed with catalytically active elements or compounds. By way of example, platinum and/or Rhodium may be electro-deposited on a shell or a functional layer without the use of external current.
If organic materials or components are used for the functional layers, polymers which are selected from the group consisting of ethylene vinyl acetate copolymers (EVA), polyamides or polyesters, but also phenolic resin, cresol resin, furan resin or epoxy resin and/or binder based on latex or rubber, are particularly suitable. By way of example, a suitable epoxy resin is known under the trade name Terokal 5051 LV, and a rubber-ba
Andersen Olaf
Bretschneider Frank
Brueckner Juergen
Hunkemoeller Paul
Schneider Lothar
Glatt Systemtechnik Dresden GmbH
Jacobson & Holman PLLC
Jones Deborah
Sperty A B.
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