Process and roller

Abstract

Method for coating a roller for a machine for the production or processing of a fibrous web, wherein the roller has a roller body onto which a metallic, ceramic and / or cermet-based coating is applied, wherein the coating of the rollers has a pore-free or non-pore-free structure, wherein the application of the coating is carried out in combination with targeted hard rolling and / or smooth rolling (roll finishing) of the coated surface, and a roller coated therewith.

Description

The invention relates to a method according to claim 1 and to a roller produced therein for a machine for the production or processing of a fibrous web. Various components in a machine for the production or processing of a fibrous web, in particular the rollers used there, are usually provided with a coating. Examples of this are described in documents WO17001657 A1, EP3112531 A1 or WO14180588 A1. For the treatment of surfaces such as the surface of rollers for a machine for the production or processing of a fibrous web, various methods are known in principle, such as roller burnishing and roller burnishing. Fixed rollers Roller burnishing (also known as burnishing) is an established cold forming process used to improve the mechanical properties and surface quality of workpieces. In this process, a hard roller or rolling tool is passed over the surface of the workpiece under high pressure. The application of this pressure plastically deforms the surface layer of material, resulting in a denser and smoother surface. Fixed rollers Roll forming can have several beneficial effects on the machined surface: 1. Increased surface hardness: Plastic deformation leads to work hardening, which increases the hardness of the near-surface layer. 2. Reduced surface roughness: The roll smooths the surface, reducing roughness and resulting in a more uniform and smoother surface. 3. Increased fatigue strength: Surface compaction closes microcracks and increases the fatigue strength of the workpiece. 4. Improved corrosion resistance: A compacted and smooth surface can exhibit better resistance to corrosion. Smooth rollers Roller burnishing (also known as burnishing or roller smoothing) is another mechanical surface treatment process that aims to reduce surface roughness and create a high-quality, smooth surface. Unlike roller burnishing, roller burnishing uses less pressure, so its main effect is to smooth the surface and improve its aesthetics. The advantages of roller burnishing include: 1. Reduction of surface roughness: The process smooths the surface, resulting in significantly reduced roughness and improved surface quality. 2. Improved surface aesthetics: A smooth, uniform surface looks and feels more appealing. 3. Improved tribological properties: A smooth surface can reduce friction and wear in moving parts, increasing the efficiency and lifespan of mechanical systems. 4. Preparation for further processing: Roller burnishing can serve as a pretreatment for subsequent coating or painting processes by creating a uniform and smooth base. These processes are designed to close pores in the roller coating, offering several advantages: 1. Pore closure: Through burnishing and / or smoothing, the surface and near-surface pores in the coatings are compacted and closed. This prevents the penetration of water and moisture, thereby improving the corrosion resistance of the roller coatings and the roller body. 2. Resource and time reduction: By reducing the need for time-consuming grinding and subsequent sealing of the coated roller surfaces, resources and processing time can be saved. This contributes to more efficient and cost-effective production. 3. Improved corrosion and wear resistance: The surface compaction achieved through burnishing and smoothing increases the hardness and reduces the roughness of the roller surface.This leads to improved corrosion and wear resistance, which in turn extends the service life of the rollers and increases the reliability of the papermaking process. 4. Prevention of agglomeration: A smoother and denser surface reduces the risk of substances from the papermaking process adhering to and agglomerating on the roller surface. This minimizes the risk of deposits and damage to the paper web, as well as to screens and felts in the production process. The implementation of fixed and / or smooth rolls in the production of rolls, particularly for paper machines, enables a more sustainable and efficient use of resources while simultaneously improving the quality and durability of the rolls. These processes represent an effective solution for optimizing the surface treatment of rolls and contribute to improving the overall papermaking process. In summary, both roller burnishing and burnishing are proven technologies for mechanical surface treatment used to improve the surface quality and mechanical properties of workpieces. While roller burnishing primarily serves to increase surface hardness and fatigue strength, burnishing focuses on reducing surface roughness and improving surface aesthetics. Both methods contribute to extending the service life and improving the performance of mechanical components and can also be used together (complementarily). Coated rollers with a non-porous structure are used in paper machines for the production of a wide variety of papers, such as packaging paper, food paper, hygiene paper, graphic papers, and many more. The coating is applied using processes such as arc spraying, HVOF, HVAF, plasma spraying, flame spraying, laser cladding, or high-speed metal arc cladding, among others. These layers have the property of causing substances from the papermaking process to agglomerate on the surface of the rollers, which can lead to problems in the manufacturing process. These problems include, among others, corrosion of the coating and / or the roller body, fouling and / or wear of the coating and / or the roller body, as well as damage to the wire, felt, or the fabric and / or paper web. To minimize these negative effects and maintain the longevity of the roller coverings and rollers, the non-porous layers are painstakingly ground to achieve the required surface finish. This grinding process also removes material that was applied beforehand (resource consumption). Following grinding and finishing, the non-porous layers are sealed to prevent the penetration of water and / or moisture during papermaking, thus preventing corrosion of the roll covering and / or the roll body. Various polymer materials are suitable for this purpose, such as epoxy resins, polysiloxane-based materials, or poly- and perfluorinated alkyl compounds (so-called PFAS substances). The aim of the invention is to improve the service life and performance of rollers in paper machines. The inventors realized that this task could surprisingly be solved by using hard rollers and / or smooth rollers. A method for coating a roller for a machine for the production or processing of a fibrous web is proposed, wherein the roller has a roller body onto which a metallic, ceramic and / or cermet-based coating is applied, the coating of the roller having a pore-free or non-pore-free structure. The application of the coating is carried out in combination with targeted hard rolling (roller burnishing) and / or smooth rolling (roller burnishing) of the coated surface. In this process, the surface and near-surface areas are plastically deformed to close the pores, increase hardness, minimize roughness, and improve wear and corrosion resistance. The stress maximum of the Hertzian contact stress is specifically consolidated within the coating to achieve these improvements. The coating thickness ranges from 30 to 2000 µm, preferably from 50 to 700 µm, and most preferably from 50 to 400 µm. The normal force applied by the tool is in the range of 100–2500 N, preferably in the range of 100–1500 N, and most preferably in the range of 200–1000 N. The zone of Hertzian contact pressure lies in the range of 10–400 µm below the surface, preferably in the range of 20–200 µm below the surface, and most preferably in the range of 50–150 µm below the surface of the contact area of ​​the tool. The processes of roller burnishing / rolling can be applied very effectively across a wide range of material classes. In particular, specific iron-based materials benefit greatly from the combination of the metastable microstructure resulting from the coating process and the plastic deformation from roller burnishing / rolling. Here, the TRIP (Transformation Induced Plasticity) and TWIP (Twinning Induced Plasticity) effects come into play. These effects allow the original, usually metastable, lattice structure to be transformed into a different crystal lattice through targeted local plastic deformation (rolling / rolling), resulting in so-called twinning. This leads to a significant increase in hardness, coupled with considerably improved wear resistance. It is advantageous if the compaction and / or smoothing is carried out immediately after application, especially in the same work step. This only marginally increases the effort and therefore the costs of coating the rollers. In particularly preferred embodiments, it may be provided that the rolling and / or smoothing is carried out in such a way that the stress maximum of the Hertzian pressure is consolidated within the coating. In the case of a multi-layer coating structure, it can be provided that the stress maximum of the Hertzian pressure is consolidated within the layer of the coating closest to the surface. Alternatively, it can be provided that the stress maximum of the Hertzian pressure is consolidated within the layer of the coating that is closest to the roller body. The maximum stress of the Hertzian contact pressure can also be consolidated at other points within the multilayer coating. Roller burnishing is frequently used in the automotive, aerospace, and mechanical engineering industries to increase the service life and reliability of components such as shafts, cylinders, and bearings. Smoothing roller burnishing is also used in various industries, including automotive, aerospace, and medical technology, particularly in the production of components with high surface quality requirements. However, no application for rollers for a machine for the production or processing of a fibrous web is known to date. In their attempts to adapt these processes for these applications, the inventors discovered several features that significantly improve both the efficiency of the process and the quality of the resulting coating. It proved particularly advantageous to perform the burnishing / rolling in the same step as the coating, thereby consolidating the maximum stress of the Hertzian contact pressure within the coating. implementation A tool (ball, small roller, cone, or similar) suitable for roller burnishing and made of a harder material than the surface to be treated is clamped in a rotary device. Parameters such as pressure, speed, feed rate, and number of passes are adjusted based on the material properties of the tool and the surface to be finished to achieve optimal results. During the roller burnishing process, the tool is rolled across the surface of the coated roller with a defined and controlled force, resulting in plastic deformation of the surface and near-surface areas. This plastic deformation closes existing pores in the coating, improving the mechanical properties of the surface and near-surface area and permanently altering the microstructure.The mechanical stress from the rolling process also increases the hardness of the coating, leading to improved wear and corrosion resistance. According to Hertz's compressive stress theorem, the zone of maximum compressive stress is not located at the contact point / contact line on the surface, but rather below the surface, i.e., within the material. Implementing hard rolls and / or smooth rolls in the production of rolls for paper machines enables more sustainable and efficient resource utilization while simultaneously improving the quality and durability of the rolls. These processes represent an effective solution for optimizing the surface treatment of rolls and contribute to improving the overall papermaking process. The invention is further explained below with reference to schematic figures. The invention is not limited to these embodiments. Fig. 1 shows a schematic representation of the roller burnishing or smoothing process over a non-porous coating according to aspects of the present invention. Fig. 2 shows a single-material and multi-material structure of the sprayed coating(s) on a roller surface according to further aspects of the invention. The proposed invention is particularly suitable for in-situ or ex-situ surface finishing applications; hot rolling / flat rolling; during or after the application of a coating to a porous coating on rollers as shown in Fig. 1. The coating can be a single material layer or a component of a multi-material structure as shown in Fig. 2. The hot rolling / flat rolling surface finishing process is specifically designed for use on rollers in paper machines, regardless of section and position. Fig. 1 shows a substrate 1 onto which a coating 2 is applied. The coating is produced, for example, but not exclusively, by processes such as arc spraying, HVOF, HVAF, plasma spraying, flame spraying, laser cladding, or high-speed metal deposition. The non-porous coating 2 of the substrate 1 is shown on the right edge of the image. A rolling tool 3 is guided over this non-porous coating 2, through which a force 4 is transmitted into the coating 2, resulting in a smoothing of the surface, minimization of roughness, sealing of the pores, and an increase in hardness through plastic deformation. This tool 3 can be, for example, a ball, a small roller, a cone, or similar. In the embodiment shown in Fig. 1, the conditions are chosen such that the maximum Hertzian contact pressure occurs within the coating 2. This has proven to be very advantageous.After treatment with tool 3, a smoothed and hardened coating 6 and surface remain after hard rolling. Fig. 2 shows a roller with a bearing journal 21. This roller has a base body 1 onto which a coating is applied. The coating can have a single-layer structure E or a multi-layer structure M. The multi-layer structure M in Fig. 2 has, by way of example, three layers. The different layers can be of the same type or different. Each of these layers can be, independently of the others, a pore-free coating 2a or a non-pore-free coating 2. Reference symbol list 1 Substrate, roller body 2 Non-porous coating 2a Porous coating 3 Tool rolling over the surface (ball, small roller, cone or similar) 4 Force application / pressure direction of the tool 5 Location of the maximum Hertzian contact pressure within the coating 6 Smoothed and hardened coating and surface after compaction 21 Bearings / journals of the roller. E Single-layer structure M Multi-layer structure QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature WO 17001657 A1

[0003] EP 3112531 A1

[0003] WO 14180588 A1

[0003]

Claims

Method for coating a roller for a machine for producing or processing a fibrous web, wherein the roller has a roller body (1) onto which a metallic, ceramic and / or cermet-based coating (2, 2a) is applied, wherein the coating of the rollers has a pore-free (2a) or non-pore-free structure (2), characterized in that the application of the coating is carried out in combination with targeted hard rolling (rolling) and / or smooth rolling (roll finishing) of the coated surface. Method according to claim 1, characterized in that the rolling and / or smoothing is carried out immediately after application, in particular in the same work step. Method according to one of the preceding claims, characterized in that the rolling and / or smoothing is carried out in such a way that the stress maximum (5) of the Hertzian pressure is consolidated within the coating. Method according to one of the preceding claims, characterized in that the coating has a layer thickness in the range of 30 - 2000 µm, preferably of 50 - 700 µm, and most preferably of 50 - 400 µm. Method according to one of the preceding claims, characterized in that the zone of Hertzian contact pressure is located in the range 10µm - 400 µm below the surface, preferably in the range 20 µm - 200 µm below the surface and most preferably in the range 50 - 150 µm below the surface of the contact area of ​​the tool (3). Method according to one of the preceding claims, characterized in that the normal force (4) of the tool (3) used is in the range of 100N - 2500 N, preferably in the range of 100N - 1500 N and most preferably in the range of 200 - 1000 N. Roller for a machine for the production or processing of a fibrous web coated by a method according to one of the preceding claims.

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