ROUND SIEVE AND ASSOCIATED MANUFACTURING PROCESS

Description

[0001] The invention relates to a method for producing a cylinder screen for a paper machine, in which a cylinder screen body that can be statically mounted in the paper machine is provided and covered with a production screen shell for the production of watermarked paper. The invention also relates to a cylinder screen manufactured accordingly.

[0002] In paper production on cylinder mold machines, a cylinder mold with a rigid production screen sleeve typically rotates in a trough containing fiber suspension, scooping paper. A vacuum is created within the cylinder mold, lowering the liquid level inside the cylinder. The fiber suspension therefore runs against the cylinder sleeve from the outside, and pulp fibers continuously accumulate on the production screen. The accumulated paper pulp is solidified to such an extent that it can be removed from the production screen as a moist paper web for further processing. Such a cylinder mold for a paper machine is known, for example, from DE 10 2006 011 621 A1.

[0003] Cylinder screens for watermarked paper production require complex manufacturing. They consist of many interconnected individual parts, which require a large amount of manual assembly. Such manufacturing naturally carries a high potential for errors. Furthermore, assembly creates joints, welds, and seams, which are usually later visible in the paper produced on the cylinder screen.

[0004] For example, it is known from GB 2533246 A that watermark areas are created using an additive manufacturing process in the form of a 3D printing process. These watermark areas are applied to the surface of the production screen shell or inserted into recesses in the production screen shell.

[0005] Based on this, the invention is based on the object of providing a cylinder screen of the type mentioned above that avoids the disadvantages of the prior art and, in particular, is easier to manufacture and has advantageous properties in paper production. The invention also aims to provide an advantageous manufacturing method for such a cylinder screen.

[0006] This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

[0007] According to the invention, in a generic method, the production screen shell is produced with a uniform shell surface, raised and / or recessed watermark areas and drainage perforations, wherein at least the shell surface of the production screen shell is formed by an additive manufacturing process as a layer sequence of a plurality of firmly interconnected material layers.

[0008] According to the invention, the outer surface of the production screen shell is initially formed unperforated by the additive manufacturing process and then, preferably by laser perforation, drainage perforations are created in the unperforated outer surface of the production screen shell.

[0009] The surface of the production screen shell is formed together with the watermark areas by the additive manufacturing process.

[0010] The surface structure of the outer surface outside the watermark areas advantageously replicates a screen structure with one or more warp thread systems and one or more weft thread systems. Particularly preferably, the surface structure of the outer surface replicates a single-layer screen structure.

[0011] In a further development of the invention, the production screen shell has two or more track areas which are formed separately by the additive manufacturing process and subsequently assembled to form the production screen shell.

[0012] The production screen shell is advantageously formed from a wire-like, powder-like, or film-like starting material, from a photosensitive paste, or a liquid. The production screen shell is particularly advantageously formed from a plastic. Additive manufacturing processes that can be considered include selective laser sintering, selective laser melting, electron beam melting, 3D printing with powder, fused deposition, laser cladding, multi-jet modeling, a PolyJet process, stereolithography, laminated object modeling, film transfer imaging, or digital light processing.

[0013] The invention also includes a cylinder screen for a paper machine according to claim 7.

[0014] The watermark regions are preferably formed integrally with the lateral surface of the production screen shell from a layer sequence of a plurality of material layers firmly bonded together in the additive manufacturing process, and the drainage perforations are formed by laser perforation of the lateral surface.

[0015] Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true-to-scale and true-to-proportion reproduction has been omitted in order to increase clarity.

[0016] They show: Fig. 1 in schematic view a cylinder screen for a paper machine for the production of security paper, Fig. 2 a section of the production screen shell in the vicinity of a watermark area in cross section along the line II-II of Fig. 1, Fig. 3 in (a) and (b) intermediate steps in the manufacture of a production screen shell, Fig. 4 in (a) and (b) intermediate steps in the manufacture of a production screen shell according to an embodiment of the invention, and Fig. 5 several tubular sections, each of which is manufactured separately by an additive manufacturing process and then assembled to form a desired production screen shell.

[0017] Figure 1 shows a schematic view of a cylinder screen 10 for a paper machine for the production of security paper. The cylinder screen 10 contains an internal cylinder screen body 12, which can be statically mounted in a paper machine. The cylinder screen body 12 is covered with a replaceable production screen jacket 14, which is configured according to the invention for the production of watermarked security paper.

[0018] For this purpose, the production screen shell 14 has a plurality of raised and / or depressed watermark areas 16 in a shell surface 32 with an otherwise uniform surface. During paper production, paper pulp locally accumulates in the watermark areas 16 with a greater or lesser paper thickness than in the surrounding vellum area, thus creating darker or lighter areas in the finished paper web. A production screen shell 14 generally contains several web areas 18 for the parallel production of a plurality of individual prints on the resulting paper web.

[0019] Figure 2 shows, for a design not according to the invention, a section 20 of the production screen jacket 14 in the vicinity of a watermark area 16 in cross section along the line II-II of Fig. 1The watermark area 16 has a high-resolution, multi-level relief 22, which can also have very sharp edges with approximately right angles in partial areas 24. Due to the multi-level relief 22, the watermark areas 16 are suitable for creating watermarks with smooth, continuous brightness transitions, but can also create sharply defined, fine details with high contrast in partial areas 24.

[0020] To ensure dewatering during paper production, the outer surface 32 of the production screen shell 14 is provided with a plurality of dewatering perforations 26 whose diameters are so small that no fibers adhere to them during paper production. Typical perforation diameters range between 50 µm and several hundred µm, for example, approximately 500 µm.

[0021] As a special feature, the entire production screen casing 14, including the watermark areas 16 and the drainage perforations 26 contained in the casing surface 32, is formed by an additive manufacturing process as a layer sequence of a plurality of firmly interconnected material layers 28, as shown in the detail section 34 of the Fig. 2 illustrated.

[0022] Additive manufacturing processes that can be considered include selective laser sintering, selective laser melting, electron beam melting, 3D printing with powder, fused deposition, laser cladding, multi-jet modeling, a PolyJet process, stereolithography, laminated object modeling, film transfer imaging, or digital light processing. Depending on the manufacturing process, the starting material can be in the form of wire, powder, foils, pastes, or liquids. The production screen shell 14 is particularly advantageously made of a plastic.

[0023] For this purpose, for example, the process of selective laser melting (SLM) can be used. In this process, the powdered plastic construction material is completely melted and hardened by a cooling process. The production screen shell 14 is built up layer by layer with the desired structure along the longitudinal axis 30 of the screen shell by successively lowering a construction platform. This can be done, for example, with the help of a 3D printing head, which, in a continuous process, prints the material layers 28 of the production screen shell 14 layer by layer as a standing tube ( Fig. 1 ) is built up. A rotary table with a vertical axis of rotation can serve as a work surface on which the print head deposits the material layers 28 revolutions per revolution as the rotary table rotates.

[0024] By manufacturing using an additive manufacturing process, the production screen shell 14 can be produced with watermark areas 16 seamlessly integrated into the shell surface 32. The watermark areas 16 can be produced, in particular, as high-resolution, multi-level watermark areas with reliefs and sharp edges with an edge width of 0.4 mm or less. The sharply edged elevations or depressions in the watermark areas, in turn, create watermarks with sharply edged light or dark motif structures during paper production. The watermark areas can have a high average spatial frequency of 2-3 Lp / mm or more, which allows the representation of the finest image details and high image sharpness in the watermark, regardless of the specific image content displayed.

[0025] At the same time, the additive manufacturing process greatly simplifies the production of the production screen shell 14 and avoids sources of error caused by the complex assembly of numerous interconnected individual parts required with conventional processes. The integrated manufacturing process completely eliminates seams, joints, and welds that are often visible in the paper when using conventional cylinder screens. The paper surface can therefore be optimally utilized. Finally, the production screen shell 14 is also mechanically very robust thanks to its integral construction.

[0026] The surface structure of the outer surface 32 of the production screen shell 14 can be largely freely selected outside the watermark areas 16 through the use of additive manufacturing processes. For example, the surface structure of the outer surface 32 can replicate a conventional screen structure with one or more warp thread systems and one or more weft thread systems. A single-layer screen layer is particularly advantageously replicated in this case.

[0027] Figure 3 illustrates an alternative, non-inventive design of a production screen jacket 40, which is initially formed with watermark recesses 42 and drainage perforations 26 by an additive manufacturing process as a layer sequence of a plurality of firmly interconnected material layers 28, as in Fig. 3(a)shown. In a further step, watermark inserts 44 are injected in the area of ​​the watermark recesses 42 directly into the shell surface 32 of the production screen shell 40 and the production screen shell 40 is thereby provided with injection-molded watermark inserts 44, as shown in Fig. 3(b) shown. In this way, watermark inserts 44 with particularly high spatial resolution or with special material properties can be introduced into the production screen shell 40. To ensure drainage in the watermark areas 16 as well, the watermark inserts 44 are also provided with drainage perforations 26.

[0028] Instead of injecting the watermark inserts 44 directly into the recesses 42, external watermark inserts can also be inserted into the watermark recesses 42, for example, by gluing them in. Furthermore, the outer surface 32 of the production screen shell 40 can also be initially produced without watermark recesses 42 and then subsequently inserted, for example, by laser cutting.

[0029] Figure 4 shows an embodiment of the invention in which the production screen jacket 50 including the watermark areas 16, but initially without drainage perforations, was formed by an additive manufacturing process as a layer sequence of a plurality of firmly interconnected material layers 28, as in Fig. 4(a)Subsequently, the production screen shell 50 is subjected to laser radiation 52 in order to produce drainage perforations 26 in the shell surface 32 by laser perforation, as in the intermediate step of Fig. 4(b) shown. Separate laser perforation may potentially result in a speed advantage in the manufacture of the production screen shell 50.

[0030] It is also possible to change the design of the Figures 3 and 4to combine and initially form a production screen shell with watermark recesses and initially without drainage perforations by an additive manufacturing process as a layer sequence of a plurality of firmly bonded material layers, and subsequently to create the drainage perforations by laser perforation of the shell surface of the production screen shell. The watermark areas can be created, for example, by directly injecting watermark inserts or by inserting external watermark inserts, as in connection with Fig. 3 already described.

[0031] Another possibility to accelerate the production of a production screen shell is to produce the production screen shell 60 in several tubular sections 62, 64, 66 separately by an additive manufacturing process, as in Fig. 5shown schematically. The tubular sections 62, 64, 66 can, for example, be printed in parallel by means of 3D printing and in particular Fig. 1 shown path areas 18 of a production screen shell 14. After their separate production, the tubular sections 62, 64, 66 are assembled to form the desired production screen shell 60. List of reference symbols

[0032] 10Round screen 12Round screen body 14Production screen shell 16Watermark areas 18Web areas 20Section 22High-resolution multi-level relief 24Partial areas 26Drainage perforations 28Material layers 30Longitudinal axis 32Shell surface 34Detail section 40Production screen shell 42Watermark recesses 44Watermark inserts 50Production screen shell 52Laser radiation 60Production screen shell 62, 64, 66Partial sections

Claims

1. A method for manufacturing a cylinder mold for a paper machine, in which a cylinder mold body that is statically mountable in the paper machine is provided and covered with a production mold shell for producing paper having watermarks, the production mold shell being produced having a uniform lateral surface, elevated and / or depressed watermark regions and dewatering perforations, at least the lateral surface of the production mold shell being formed through an additive manufacturing method as a layer sequence of a plurality of material layers that are firmly bonded together, characterized in that through the additive manufacturing method, the lateral surface of the production mold shell is first formed unperforated, and subsequently, preferably through laser perforation, dewatering perforations are produced in the unperforated lateral surface of the production mold shell, and in that the lateral surface of the production mold shell is formed together with the watermark regions through the additive manufacturing method.

2. The method according to claim 1, characterized in that the surface structure of the lateral surface outside of the watermark regions reproduces a mold structure having one or more weft thread systems and one or more warp thread systems.

3. The method according to at least one of claims 1 to 2, characterized in that the production mold shell comprises two or more web regions that are formed separately through the additive manufacturing method and thereafter are assembled to form the production mold shell.

4. The method according to at least one of claims 1 to 3, characterized in that the production mold shell is formed from a starting material in wire form, powder form or foil form, from a photosensitive paste or from a liquid.

5. The method according to at least one of claims 1 to 4, characterized in that the production mold shell is formed from a plastic.

6. The method according to at least one of claims 1 to 5, characterized in that selective laser sintering, selective laser melting, electron beam melting, 3-D printing with powder, fused deposition modeling, laser metal deposition, multi-jet modeling, a PolyJet method, stereolithography, laminated object modeling, film transfer imaging or digital light processing are used as the additive manufacturing method.

7. A cylinder mold for a paper machine having a cylinder mold body that is statically mountable in the paper machine and a production mold shell for producing paper having watermarks, manufacturable according to one of claims 1 to 6, in which the production mold shell comprises a uniform lateral surface, elevated and / or depressed watermark regions and dewatering perforations, and at least the lateral surface of the production mold shell is formed from a layer sequence of a plurality of material layers that are firmly bonded together in an additive manufacturing method, the watermark regions are formed integrally with the lateral surface of the production mold shell from a layer sequence of a plurality of material layers that are firmly bonded together in the additive manufacturing method, and the dewatering perforations are formed through laser perforation of the lateral surface.