Facsimile and static presentation processing – Facsimile – Recording apparatus
Patent
1992-09-14
1996-01-23
Wong, Peter C.
Facsimile and static presentation processing
Facsimile
Recording apparatus
H04N 121, H04N 123
Patent
active
054869285
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for manufacturing a stamp to be used in embossing the wire cloths of a papermaking machine, for instance a wire cloth suitable to make watermarks. The stamp may be in the form of a tool with which to directly emboss the wire cloth or it may be a master stamp used to directly make other stamps by electroforming.
The invention also concerns the equipment with which to implement such a method.
Watermarked paper, for instance fiduciary paper, in particular for banknotes and for deluxe letterhead, is made in a round form, or in a Fourdrinier machine which conventionally comprises several wire mesh cloths which are superposed and allow drip-draining the cellulose-fiber suspension from which the paper is made. As a rule two cylindrical wire cloths are used that comprise depressed and/or raised embossings to achieve variable fiber densities as a result of which watermarks are achieved.
As a rule the wire-cloth embossing is made by an embossing tool or stamp which is made from copper or nickel, in general by electroplating.
When it is desired to reproduce a drawing in the form of a watermark, an artist makes a rendering of the drawing. Next, the artist makes a wax engraving of this drawing. Such an engraving may take fifteen days of the watermark-artist's time. Next a replica of the wax engraving is made from a polymerizable material. Then the replica is rendered conductive and immersed into an electroplating bath to obtain a matching design and lastly a copper or nickel stamp is electroformed.
Such manifold operations obviously are lengthy and delicate.
Accordingly attempts have been carried out in the prior art to stamp wire cloths of a round form by spark or electro-erosion machining. Such a procedure is described in the European patent application EP A 252,842 filed by Banque de France. In this document, a steel tool is made with which to emboss wire cloth forms of a round form using an electrode for electro-erosion. This electrode is engraved by machining plane after plane. This is a graphite electrode and the machining is level by level. Illustratively, to achieve an engraving depth of 20 mm by this procedure, forty passes are needed. Accordingly, to achieve an engraving depth down to 20 mm, a machining time of about 60 hours will be required.
Therefore any procedure to solve the problem of long manual operations when making a steel tool will only partly achieve its objectives.
Moreover and as mentioned in this document, a part is used which is made of graphite, and is hence fragile.
The electro-erosion technique entails using a dielectric liquid, for instance a very fluid oil of low volatility and having a high flash point. This is kerosene.
In said procedure, furthermore, the distance between the electrode and the part being machined must be kept at the dielectric thickness which the electric discharges can cross. Maintaining this specific distance between electrode and part may render both the procedure and the equipment complicated.
The Canadian patent 1,003,049 describes a manufacturing procedure for a metal badge made by electro-erosion. This badge is planar, that is, two-dimensional. The European patent document EP A 252,842 describes a means for making a three-dimensional graphite electrode. This means consists in engraving along several planes that are increasingly deeper. Thus a first engraving pass is carried out, then a second, then the nth. This is discontinuous engraving.
European patent application EP A 273,826 describes an automated engraving procedure for small ornaments or small tools. The object of this procedure is to faithfully show the distinctive features of a given subject. This procedure consists of the following: representing the engraving to be made in such a manner that sequences of digital signals shall be generated that control the relative displacements of an outline and of an engraving tool with three displacement axes X, Y and Z, said secondary series consisting of binary signals, two contiguous binary signals defining an original segmen
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Bigot Etienne
Doublet Pierre
Passebecq Claude
Arjo Wiggins S.A.
Gibson Randy W.
Wong Peter C.
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