Stock material or miscellaneous articles – All metal or with adjacent metals – Having variation in thickness
Reexamination Certificate
2000-07-26
2002-08-20
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having variation in thickness
C428S610000, C428S687000, C148S903000, C148S512000, C219S121640, C219S121660
Reexamination Certificate
active
06436553
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an endless steel band, particularly such a band comprised of austenitic and/or martensitic steel, having at least one weld seam, for use in double-band pressing; and a method of surface structuring of such an endless steel band.
BACKGROUND OF THE INVENTION
In the manufacture of planar objects, e.g., surface-coated particle board, or panels comprised of resin-impregnated fibers (e.g. with melamine resin), or all-plastic panels (e.g. comprised of polyacrylates or polycarbonates), the desired surface properties, and the bonding of the layers in a laminated product, can be achieved with the use of presses, particularly hot presses. It is known to use a double press for this purpose, having an upper and lower press plate. At least one of these press plates has the desired surface characteristics. To increase the productivity of a press, so-called stacked presses have been developed, wherein a plurality of press plates are superposed, with the regions between the press plates used to accommodate the material which is to be pressed. In this way, a substantial number of panels can be formed in a single pressing operation.
Different surface characteristics can be conferred upon the press plates. Thus it is possible for the press plates to have a highly polished surface, imparting a smooth planar surface to the product. For some applications it may be desirable for the surface to be structured, e.g. in a wood-grain pattern, or with an artistic relief. For this purpose, it is known, in analogy to the manufacture of offset press plates, to apply a photosensitive coating to the press plate, which then is exposed to light. Then, depending on the particular process variant employed, either the photo-exposed or -unexposed region is sensitive to an etchant, and the other region is inert; wherewith the photoexposure provides the basis for patternwise etching. This method enables, e.g., three-dimensional reliefs to be fabricated on the surface of a press plate, which reliefs correspond to natural or artificial designs.
Another method of structuring the surface of a press plate is described in Eur. Pat. 0,536,625 A1, according to which a continuous or pulsed laser beam is used to locally remove material over the surface of a mold or a press plate. In order to generate a natural-appearing relief surface, e.g. simulated leather in a pressed plastic article (the final product produced from said mold or press plate), the movement of the laser beam over the (press plate) workpiece surface is coordinated by a random number generator. Another application of this method is in the manufacture of prostheses which are to be integrated into animal or human tissue.
So-called double-band presses have been developed, to improve product quality and production productivity. These have an upper and lower band, which may be comprised of steel, which bands are moved in the same direction at the same speed, providing uniform transport of the workpiece material, which material is disposed in a generally plate-shaped gap between the two bands (which may be endless bands). Such a double-band press is described, e.g., in U.S. Pat. No. 3,884,749. Endless bands in the required thickness and extent, and with the required flexibility, are costly to fabricate; therefore the customary fabrication method is to weld together a plurality of individual sheets having a thickness of 1-3 mm. The welds joining successive such sheets in the longitudinal direction are designated “transverse welds” (to describe the general direction of extent of the weld seam), and the welds (if any) joining neighboring sheets in the transverse directions are designated “longitudinal welds” (the longitudinal direction being the direction of circulation of the band, and the transverse direction being the direction lateral to said circulation direction). It is also possible to have welds with circular or other generally smooth (but closed) contours of extent, employed in patching damaged (or defective) regions. In fabricating a completely smooth planar surface (which is polished or ground), the weld seams generally do not present inhomogeneities.
It is well known that weld seams respond differently to corrosive agents than does the basic material, even if the seams nominally have the same chemical composition as said surrounding material. In the case of weld seams wherein the weld has been produced with added materials, three zones are identifiable which have different properties; viz.:
the added weld material which has been melted during the welding;
the basic material which has been fused during the welding, which basic material was part of the original object to be welded; and
the zones of the basic material which have been influenced by the heat of the welding process.
When endless welded, “seamless” steel bands are etched, the weld seams give rise to loci of nonuniformity, which detract from the appearance of the ultimate product produced by the pressing of said bands against a workpiece.
In order to avoid the aforementioned drawbacks, it was proposed, according to Ger. Pat. 3,337,962 C2, to apply an overlayer configured as an electrically nonconducting relief design representing raised and depressed bare metal areas, and then to carry out electrolytic removal of metal. Such a method allows weld seams to be covered but the result is not a homogeneous strip, because in general the material removed is not identical with the underlying support material but tends to be softer. Thus there is a risk that the overlayer will be forced (or worn) away from the surface during use. For an endless band which is mounted around rollers, the outermost layer (or coating) of the band is subjected to the maximum stresses and (as mentioned) is generally softer than the steel strip, so that the service life of such a coated product is substantially less than that of a normal steel band.
The state of the art (closest art to the present invention) is represented by Eur. Pat. 0,031,613 B1, in which a different method of manufacturing a relief pattern on an endless band to be used as a pressing pattern is described. The endless band is provided with a galvanically applied metal coating layer, and an etching process is carried out on said coating. This method can be arranged to eliminate the effect of the weld seam on the final product; however, as a rule the applied metal layer is a metal which is softer than the underlying steel support strip, e.g., copper. When the applied layer is subjected to the strong influences of compressive and tensile stresses it tends to at least partly become forced away, thereby creating undesired loci of inhomogeneity.
SUMMARY OF THE INVENTION
It is an objective of the present invention to devise an endless steel band wherein weld seams, finished surfaces and structured surfaces do not display visually apparent loci of inhomogeneity; wherein the working surfaces have essentially analogous properties, e.g. hardness, to the properties of the underlying steel band; and wherein viewed over the cross section the surface structures have a high homogeneity and have a visually apparently continuous transition to the remainder of the steel band.
The inventive endless steel band, particularly such a band comprised of austenitic and/or martensitic steel, having at least one weld seam extending transversely to the longitudinal direction of the band, said inventive band being intended for use in double-band pressing, has at least one first surface layer which generally extends over the entire area of the steel band, which first surface layer has a different composition from an intermediate layer which intermediate layer also generally extends over the entire extent of the strip and is disposed between said first surface layer and a second surface layer which second surface layer is at the opposite surface of the strip from said first surface layer; and the subject steel band has the following essential characteristics: said first surface layer is comprised of the steel of the steel band, and in particular has
Schuster Roland
Stadler Otto
Berndorf Band GesmbH
Jacobson & Holman PLLC
Zimmerman John J.
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