Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-06-30
2003-06-17
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C277S651000, C277S654000, C219S121640, C428S594000, C428S607000
Reexamination Certificate
active
06579626
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to metal-reinforced layered composites based on one or more soft materials, in particular to gaskets, gasket sheets and metal layers, as well as to a method of manufacturing the same.
The metal-reinforced layered composites according to the invention have at least one intermediate metal layer. The intermediate metal layer includes at least two at least partially overlapping metal foils which are joined to one another in an overlap area. The invention makes it possible to manufacture large-dimension laminated panels which, as gasket sheets, meet the highest technical standards. Gaskets, in particular flat gaskets in annular form, as shown in
FIG. 9
, are manufactured by being punched out of the gasket sheets.
Layered composites based on one or more soft materials are often reinforced with thin metal foils to improve their mechanical stability. The soft materials used in layered composites include thermoplastics, above all PTFE-based thermoplastics, and elastomers which may be reinforced with inorganic or organic fibers, such as e.g. aramide, carbon, ceramic and metal fibers. The compressive strength of the soft materials may also be increased by fillers such as e.g. silicon dioxide, aluminum oxide, carbon or graphite in powder form. Furthermore, inorganic and compression-proof materials such as, in particular, mica and graphite may be used as soft materials. Foils and laminates manufactured from expanded graphite, which are jointly referred to below as graphite foils, are also used as special graphite variants. Corresponding layered composites are described, for example, in German Published, Non-Prosecuted Patent Application DE 198 04 283 A1, corresponding to U.S. application Ser. No. 09/244,836 now U.S. Pat. No. 6,258,457. Besides simple metal foils it is also possible to use spiked metal sheets as intermediate metal layers. The spiked metal sheets have spikes which may extend to one or to both sides. In the simplest case, a metal-reinforced layered composite based on one or more soft materials includes a metal foil layer embedded in two soft material layers.
The metal foils are commercially available only up to a limited web width which depends on the material and foil thickness. It is necessary to join together at least two metal foils for the intermediate metal layer to manufacture metal-reinforced layered composites or gasket sheets of such dimensions that the web width of the available metal foils is insufficient to allow the intermediate metal layers of the layered composites to be removed from a metal foil web in one piece.
Until now, such commercial-scale metal-reinforced layered composites have been realized by overlapping metal foil webs at their lateral ends and effecting joining together either by gluing, mechanical interlocking or welding, such as by resistance roll seam welding. The metal foils used for the intermediate metal layer in the layered composites mostly have a small thickness, such as e.g. 50 &mgr;m or 100 &mgr;m, in order to make it easy to punch gaskets out of the layered composites. Therefore, it is generally impossible to carry out butt welding of the metal foils under industrial production conditions.
A method and an apparatus for welding together butt-jointed sheets is known from German Published, Non-Prosecuted Patent Application DE 195 29 542 A1. That method is based on the sheets to be welded together initially overlapping in their marginal region. The overlapping end zones of the marginal regions are then cut off with mutually aligned cut edges, the cut edges are then made to abut one another and finally the cut edges are welded to one another by a laser beam. As a result of that time sequence of process steps, it is impossible, particularly with long webs which are moving, to guarantee that the cut edges at right angles to the direction of motion of the webs will still be in the same position when they reach the welding location as they are when they are cut. Even minor external influences, such as temperature variations or vibrations, as well as tiny undulations in the thin metal foils, may lead to gaps between the cut edges of the webs or a renewed overlap of the webs. A remedy therefor is provided according to the method described in the German Published, Non-Prosecuted Patent Application mentioned above. That is accomplished in the case of long webs and/or large web widths by a guide body which stabilizes the position of the webs relative to one another. That guide body guides the sheet metal webs, which are to be welded together, in such a way that the lateral edge of the webs lies against the base of a slot in the guide body. However, in the case of the metal foils which are used in the layered composites of the gasket sheets, their low thickness of, at times, well below 0.25 mm precludes such guidance by a guide body on a commercial scale. As the metal foil webs move through the guide body, high forces at the base of the guide slot act upon the lateral edge of the metal foil. Due to low stability thereof, those forces are sufficiently high to cause buckling very rapidly and therefore to cause the edge of the foil to be destroyed or even to caused the metal foil to tear. That might be counteracted by a very narrow guide slot but that might lead to the metal foil becoming stuck in the guide slot and therefore possibly tearing. The use of such a guide slot may, moreover, cause the metal foil web to be displaced in such a way as to form a slight undulation or fold in the metal foil web which causes the foil web guidance downstream of the guide slot to run off in an uncontrolled manner. It is therefore impossible to use the butt-welding method described in German Published, Non-Prosecuted Patent Application DE 195 29 542 A1 for the particularly thin metal foils such as are normally used in layered composites for gasket elements.
Heretofore, various techniques have been used to join metal foils for intermediate metal layers for gasket sheets, wherein foil ends overlap in the region of the joint.
In one instance, joining is effected by applying an adhesive, such as e.g. epoxy resin, which hardens, between the overlapping foil ends. In that case, the adhesive is mostly applied over the entire overlap region on at least one of the metal foils which are to be joined. Gluing together of the metal foils has the drawback of only permitting gaskets which are manufactured from layered composites including intermediate metal layers joined in that manner to be used in an extremely limited temperature range. The reason for that limitation is that, at higher temperatures, the adhesive softens and/or is partially thermally decomposed. On one hand, that may lead in the gaskets to the metal foils shearing off more easily from one another at their glued junction points under stress, such as tensile forces in the direction of the metal foils and compressive forces at right angles to the intermediate metal layers, thereby reducing the mechanical stability of the gaskets. Only porous, leaky, pyrolized residues of the adhesive remain in the overlap region between the glued metal foil ends as a result of thermal decomposition of the adhesive. If the pores being produced in the adhesive merge with one another, that may produce extensive continuous channels in the glue residue. The channels in a gasket may even extend from one edge of the gasket to the other and lead to a substantial increase of the leakage rate of the gasket because a medium, which is to be sealed off, may escape out of the gasket through those channels. Such channels, which extend from one gasket edge to the other gasket edge, are referred to below as leakage channels of the gasket. Gaskets having intermediate metal layers, which include metal foils glued to one another, therefore tend to have higher leakage rates at increased temperatures. The use of gaskets, which have intermediate metal layers being formed of metal foils glued to one another, is additionally restricted to media which do not attack the adhesive.
Jung Manfred
Öttinger Oswin
Greenberg Laurence A.
Locher Ralph E.
SGL Carbon AG
Stemer Werner H.
Zimmerman John J.
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