Laser machined squeegee

Abstract

The invention relates to a method for processing a doctor blade, in particular a doctor blade for wiping printing ink off a printing cylinder, comprising a flat and elongated main body made of carbon steel, which has a fastening region and a working edge formed in a longitudinal direction, wherein an edge layer of the working edge of the doctor blade is cured using a laser light beam at least in one section to be processed.

Description

Technical area

[0001] The invention relates to a method for machining a doctor blade, in particular a doctor blade for doctoring printing ink from a printing cylinder, comprising a flat and elongated base body made of carbon steel with a fastening region and a working edge formed in a longitudinal direction. The invention further relates to a doctor blade with a working edge machined in at least one section. State of the art

[0002] Doctor blades are used in the printing industry as well as in paper production.

[0003] In the printing industry, doctor blades are primarily used to remove excess printing ink from the surfaces of printing cylinders or rollers. The quality of the doctor blade has a decisive influence on the printing result, especially in gravure and flexographic printing. Unevenness or irregularities in the working edges of the doctor blade that come into contact with the printing cylinder, for example, lead to incomplete removal of the printing ink from the lands of the printing cylinders. This can lead to uncontrolled ink release onto the printing substrate.

[0004] During wiping, the working edges of the doctor blade are pressed against the surfaces of the printing cylinders or rollers and are moved relative to them. Thus, the working edges, especially in rotary printing presses, are exposed to high mechanical stress, which results in corresponding wear. On the other hand, the working edges of the doctor blade are subject to high demands to ensure precise wiping over the longest possible period of use. Doctor blades are therefore fundamentally consumables that must be replaced periodically. Therefore, it is important to keep manufacturing costs low while simultaneously maximizing the service life, especially while maintaining consistently high doctor blade quality.

[0005] Squeegees are usually based on a steel or plastic squeegee body with a specially shaped working edge. To improve the service life of the squeegee, the hardness of the working edges can be adjusted and / or coated with plastics, paints, metals, and / or hard materials. The structural and material composition of the squeegee significantly influences its mechanical and tribological properties.

[0006] Such a doctor blade is described, for example, in EP 0 911 157 B1. This relates to a doctor blade for removing excess printing ink from the surface of a printing form. To minimize wear on the surface of the printing form in contact with the doctor blade, the blade and the area of ​​the rear doctor blade part adjacent to the blade are coated over the entire length of the blade with a lubricant or at least with lubricant particles. The coating can comprise a carrier material in which both lubricant particles and particles of a wear-resistant material are embedded.

[0007] DE 10 2013 011 275 A1 describes a doctor blade which, on its outer surface in the area of ​​the working edge, has a section facing the printing roller with an ink-friendly surface, and an adjoining section with an ink-repellent property. This allows the printing ink to spread better on the more ink-friendly section, thus improving print quality. Both sections can be produced by processing the material of the base body. For example, the ink-friendly section can be roughened by sandblasting, etching, laser engraving, electron beam irradiation, or grinding to create or enhance its ink-attracting properties.

[0008] However, such squeegees are still not entirely satisfactory in terms of manufacturing costs and precision when wiping.

[0009] In the paper industry, doctor blades are also referred to as coating knives, coating blades, or coating knives, depending on their application. A doctor blade or doctor blade can be used to remove excess coating color (e.g., pigments, binders, additives, etc.) from a paper substrate or paper web. As in the printing industry, the service life of doctor blades, coating blades, or coating knives can be improved by modifying their working edges.

[0010] WO 2006 / 007984 A1 describes, for example, cold-rolled steel strips used for the production of coating knives, application knives and I <reppschabern verwendet werden, welche eine verbesserte Lebensdauer aufweisen. Dies wird durch eine spezielle Stahlzusammensetzung und die Verwendung eines pulvermetallischen Verfahrens erreicht, welches zu einer Zusammensetzung mit einem hohen Karbidanteil führt. Zudem kann die die Arbeitskante durch einen Laserstrahl gehärtet werden.

[0011] Furthermore, WO 92 / 06796 A1 describes doctor blade elements designed in particular for etching paper or cardboard. A special blade design is provided, which allows for greater variation in contact pressure in order to apply a wider range of coating weights. It is also mentioned that the blade can be additionally hardened in the area of ​​the metering bevel surface by means of a temper hardening or laser hardening in order to increase the modulus of elasticity. The hardness on the surface should be lower than in the underlying areas so that the blade can adapt better to the paper or the counter roll during the grinding-in phase. Also mentioned is the introduction of cross-sectional changes to the blade in the form of grooves, which can also be created using laser light, among other things.

[0012] However, even in the area of ​​doctor blades for the paper industry or for paper production, the known systems are not entirely convincing.

[0013] There is therefore still a need for improved doctor blades for printing technology as well as for paper production, which have fewer or no disadvantages of the above-mentioned. Description of the invention

[0014] The object of the invention is to provide improved methods for producing doctor blades for printing technology and paper production, belonging to the aforementioned technical field. In particular, methods are to be created that enable the most economical production of doctor blades. Another object of the invention is to provide advantageous doctor blades that can be produced as economically as possible and exhibit the best possible wear resistance for applications in printing technology or paper production. In particular, the doctor blades should simultaneously enable the most precise possible spreading of printing or coating inks.

[0015] These objects are achieved by the features of independent claims 1 and 9.

[0016] In a first aspect, the invention relates to a method for machining a doctor blade, comprising a flat and elongated base body made of carbon steel with a fastening region and a working edge formed in a longitudinal direction, wherein an edge layer of the working edge of the doctor blade is hardened at least in a section to be machined with a laser light beam, which is a pulsed light laser beam.

[0017] The term "doctor blade" is to be understood broadly here and includes both doctor blades for applications in the printing industry and the paper industry. In particular, doctor blades are printing doctor blades, doctor blades, doctor blades, and / or coating blades. In a particularly preferred embodiment, the doctor blade is a printing doctor blade, which is specifically designed for doctoring printing ink off a printing cylinder.

[0018] The term "doctor blade" includes both individual, ready-to-use, pre-cut doctor blades and so-called endless doctor blade belts, which can be cut to length later to form multiple individual blades. "Endless doctor blade belts" in this context refer to doctor blade belts with a length of at least 5 m, in particular at least 10 m, and especially at least 50 m. For example, the doctor blade belt can have a length of 100 m. In a particularly preferred embodiment, the method according to the invention is carried out using endless doctor blade belts.

[0019] "Carbon steel" is also known as C-steel and is defined as unalloyed quality steel according to DIN EN 10020:2000. Specifically, this steel grade has a carbon content of 0.2 to 0.65 wt.%. The proportions of other alloying components are below a limit specified by the standard. In particular, the carbon steel has the following limit values ​​or maximum proportions: aluminum: 0.30 wt%, boron: 0.0008 wt%, bismuth: 0.10 wt%, cobalt: 0.30 wt%, chromium: 0.30 wt%, copper: 0.40 wt%, lanthanides (each counted individually): 0.10 wt%, manganese: 1.65 wt%, molybdenum: 0.08 wt%, niobium: 0.06 wt%, nickel: 0.30 wt%, lead: 0.40 wt%, selenium: 0.10 wt%, silicon: 0.60 wt%, tellurium: 0.10 wt%, titanium: 0.05 wt%, vanadium: 0.10 wt%, tungsten: 0.30 wt%, others (excluding C; P; S and N) each 0.10 wt%.

[0020] In this case, “hardness” refers to the Vickers hardness determined according to DIN EN ISO 6507-1:2018 to -4:2018.

[0021] It has been demonstrated that the use of a laser light beam can achieve a temporally and spatially controlled energy input into the section of a conventional carbon steel doctor blade to be processed. This enables locally limited hardening, unlike other hardening methods. This is also possible without the need for expensive alloy steels. Carbon steel doctor blades are easy to harden using laser light beams and, at the same time, exhibit excellent mechanical properties for applications in printing technology and paper production.

[0022] Curing with a laser light beam makes it possible, in particular, to leave the base body of the squeegee unaltered and only process the working edge in the desired areas. The section of the squeegee to be processed can be hardened from the edge area down to deeper areas below the surface. Depending on the process parameters and the structure of the squeegee, only the edge area can be hardened, or the underlying areas of the squeegee can also be hardened. This allows the mechanical properties of the squeegee to be specifically adapted and controlled.

[0023] During the processing process, the targeted processing with laser light beams allows the energy input to be controlled in such a way that, despite the curing, undesirable deformation of the squeegee during processing or the curing process is prevented. This is one of the major advantages of the present invention. Accordingly, the squeegees have clearly defined working edges even after the processing process.

[0024] The process is also very flexible, as it can be used for different doctor blade types or geometries by adjusting the process parameters. Due to the ability to process endless doctor blade belts, the process also allows for very cost-effective doctor blade processing, as the blades can be hardened in a further process step directly after production, for example.

[0025] Particularly preferably, the laser light beam is moved continuously over the section to be machined on the working edge during processing.

[0026] "Continuously moved" in this case means that the laser light beam is moved without interruption during processing, preferably at a constant speed, over the entire area of ​​the working edge to be processed.

[0027] The movement of the laser light beam over the section to be processed can in principle be achieved (i) by a spatial movement of the squeegee with a fixed laser light beam, (ii) by a spatial movement of the laser beam, for example by a deflection optics, with a fixed squeegee or (iii) by a simultaneous spatial movement of the squeegee and laser beam.

[0028] It has been demonstrated that the continuous movement of the laser light beam across the section of the working edge to be processed can achieve a particularly uniform energy input into the section of the squeegee being processed. At the same time, the continuous relative movement can achieve a stable balance between energy input and heat dissipation, e.g., via the non-processed areas of the squeegee, via heat radiation, and / or through additional cooling devices. This can also prevent unwanted deformation of the squeegee during processing or the curing process.

[0029] According to an advantageous embodiment, the process parameters and / or the movement of the laser light beam during processing over the section to be processed on the working edge are controlled in such a way that deformation of the doctor blade is reduced or prevented.

[0030] Preferably, the relative speed between the laser light beam and the working edge in the longitudinal direction during processing is 0.5–5 m / min, particularly 0.8–4 m / min. This enables fast yet reliable processing of the working edge.

[0031] The laser beam's power is preferably between 5 and 50 W, especially between 10 and 30 W. This allows for effective hardening of materials typically used for doctor blades, such as steel. However, lower or higher power levels may be suitable for other materials or special doctor blades.

[0032] The light of the laser beam is particularly preferably UV light, visible light, or infrared radiation. The wavelength of the light is, for example, in the range of 150 nm - 3 µm, preferably 400 nm - 2.5 µm, and especially 500 nm - 1.5 µm. Especially at short wavelengths, the surface of the working edge can be additionally structured during processing by ablation. Longer wavelengths are particularly suitable in cases where no additional structuring or ablation-free structuring is desired.

[0033] The laser light beam according to the invention is a pulsed laser light beam. A pulsed laser light beam has a pulsating intensity of the light waves.

[0034] Surprisingly, the use of pulsed light laser beams offers several advantages in this case. For example, the energy input into the section being processed can be controlled more precisely. This allows, for example, the edge layer to be specifically hardened while the underlying areas retain their original hardness. It is also possible, for example, to create a gradual decrease in hardness from the edge area toward the underlying areas. This can be achieved without causing significant deformation of the squeegee.

[0035] Furthermore, the use of a pulsed light laser beam enables targeted structuring of the surface of the working edge. This allows, for example, the surface tension of the working edge to be specifically adjusted, or in particular reduced. It has been shown that this, in combination with the increased hardness, leads to a significant increase in the wear resistance of the doctor blade while simultaneously improving its wiping properties.

[0036] Without being bound by theory, it is assumed that the structuring of the surface, in combination with the increased hardness in the printing process, leads to reduced system friction between the squeegee, cylinder, and printing ink. The reason for this is suspected to be that the structuring of the surface results in a reduction in surface tension, which in turn is likely to lead to the molecules of the printing ink interacting more strongly with each other than with the working edge of the squeegee. This appears to result in lower fluid friction between the squeegee and the printing ink.

[0037] Negative application-related effects that arise during the printing process between the squeegee and the printing ink have also been minimized. In particular, all application-related errors caused by the Barus effect and the Coanda effect have been minimized.

[0038] According to a preferred embodiment, the pulse parameters of the pulsed laser light beam are selected such that local hardening of the edge layer is achieved and / or periodically distributed depressions and / or elevations are formed in the surface of the edge layer. Particularly preferably, both the edge layer is hardened and the surface is structured by periodically distributed depressions and / or elevations.

[0039] Particularly preferably, the method is carried out in such a way that the laser light beam scans the working edge of the doctor blade, at least in the section to be processed, in particular in at least two mutually perpendicular spatial directions. This allows targeted structuring to be introduced into the working edge and the hardness to be increased. Scanning can be achieved, for example, by X-deflection units for deflecting and focusing laser beams in one dimension or by XY deflection units for deflecting and focusing laser beams in two dimensions. So-called galvanometer scanners with mirrors are suitable, for example.

[0040] The scanning speed of the laser light beam is preferably 1,000 - 10,000 mm / s.

[0041] The repetition rate of the laser pulses is, for example, 100 - 500 kHz.

[0042] The focal diameter of the pulsed laser beam at the point of impact on the squeegee is preferably 1-100 µm, especially 10-50 µm. This allows for the creation of relatively fine structures in the surfaces of the working edge, and the hardening of the working edge can be defined very precisely.

[0043] Preferably, the method is controlled by a control unit, wherein the control unit coordinates and controls the relative speed between the laser light beam and the working edge, the scanning speed, the pulse duration and / or the repetition rate of the laser light beam.

[0044] According to a preferred embodiment, the working edge of the doctor blade is processed with the laser light beam in such a way that a side opposite a processed side of the working edge remains unprocessed. In other words, the doctor blade is processed on a first side and possibly on the front side, but not on the second side of the working edge opposite the first side.

[0045] As has been shown, the side of the working edge which was first structured and / or hardened with the laser can lose at least some of the previously gained hardness when the opposite side is machined due to the renewed introduction of thermal energy into the substrate.

[0046] To circumvent this effect, both sides can be processed simultaneously, ensuring that the energy input is evenly distributed over time. In this case, it may be useful to reduce the energy input and / or increase the relative speed between the laser light beam and the working edge to avoid deformation of the squeegee. However, this has the disadvantage that the surface structuring and the edge layer depth can only be controlled to a limited extent. This disadvantage can be neutralized by using a cooling system.

[0047] Deformations during simultaneous machining of both sides of the working edge are likely to be due to the fact that the simultaneous energy input of thermal energy into the substrate on both sides is twice as high as the comparable time-delayed energy input into the substrate.

[0048] However, empirical data show that single-sided surface structuring and / or surface hardening of the working edge is entirely sufficient in terms of wear resistance and wiping behavior if the side of the working edge facing the printing cylinder is treated according to the invention. No disadvantages were found compared to a doctor blade with double-sided treatment. However, doctor blade processing is significantly simplified and more economical.

[0049] According to advantageous methods, the doctor blade is continuously unwound from a supply reel during processing, processed with the laser light beam on the top or bottom side while unwound, and then preferably wound up on a separate take-up reel. This allows already wound endless doctor blade strips to be processed at any time. However, the actual processing takes place in the unwound state, which has the advantage that the working edge is accessible from all sides.

[0050] It may be advantageous to unwind two squeegees parallel to each other from a supply reel, guide them parallel to each other in the unwound state, process them with the laser light beam on the top or bottom, and then wind them up, preferably on a separate take-up reel. The squeegees are preferably guided next to each other so that the working edges to be processed face each other. This has the advantage that the laser light beam can process both squeegees simultaneously, which can, in particular, increase throughput. In principle, the two squeegees can be processed with identical or different parameters.

[0051] In a further and particularly advantageous embodiment, the doctor blade is processed in a rolled state. It is possible, for example, to wind the doctor blade onto a cylindrical winding body.

[0052] Processing in a roll-like state minimizes space requirements. On the other hand, the doctor blade forms a compact body made up of stacked layers. This allows the heat generated during processing to be effectively distributed and dissipated, reducing or preventing the problem of deformation.

[0053] Preferably, the squeegee is wound spirally and, in the form of a cylinder, is processed with the laser light beam from a direction parallel or oblique to the cylinder axis. This allows the squeegee to be processed particularly in the area of ​​the front side of the working edge. In particular, it is also possible to process several sections of the working edge simultaneously.

[0054] In particular, the spirally wound doctor blade is rotated around the cylinder axis during processing and preferably at the same time the laser light beam is moved along a diameter line of the cylindrically wound doctor blade, in particular in such a way that the laser light beam processes the working edge of the wound doctor blade along the entire longitudinal length.

[0055] According to a further advantageous embodiment, two separate doctor blades are wound spirally into each other in the form of a cylinder, rotating in opposite directions. The two doctor blades are preferably aligned so that the working edges of the two separate doctor blades face away from each other when wound. The working edge of one doctor blade is then part of one end face of the cylinder, while the working edge of the second doctor blade is part of the opposite end face of the cylinder.

[0056] Preferably, both ends of the cylinder are machined from a direction parallel or oblique to the cylinder axis using laser light beams from two separate laser light sources. This allows both squeegees to be machined simultaneously. In this case, it is possible to machine the squeegees using identical or different parameters.

[0057] A further and particularly advantageous embodiment provides for the doctor blade to be wound helically around the outer surface of a cylindrical winding core, so that the working edge of the doctor blade forms a conical spiral and is at least partially exposed along its entire wound length from a direction perpendicular to the outer surface of the winding core. Depending on the pitch of the formed conical spiral, a larger or smaller portion of the working edge is exposed.

[0058] Preferably, the squeegee is processed with laser light from a direction perpendicular or diagonal to the outer surface. This allows the working edge to be processed from the front and / or in the area of ​​the underside or top of the squeegee.

[0059] Specifically, the winding core with the helically wound doctor blade rotates around the cylinder axis during processing, and at the same time, the laser light beam is moved in a direction parallel or oblique to the cylinder axis. This allows the laser light beam to process the working edge of the wound doctor blade along its entire longitudinal length.

[0060] If a winding core is present, one possible design involves cooling it with the laser light beam during processing. This can further increase and control heat dissipation. However, cooling is not mandatory.

[0061] Furthermore, it may be preferred if the working edge of the doctor blade is coated with an additional coating, at least in the processed section, after processing with the laser light beam. This can be, for example, a wear-reducing and / or friction-reducing coating. The coating can be, for example, a metal coating, a hard material coating, a ceramic coating, or a polymer coating. With such coatings, the doctor blade can be further adapted for specific applications. As has surprisingly been shown, a doctor blade with a surface structure according to the invention can form an adhesive layer and / or intermediate layer, so that the additional coating adheres better.

[0062] A second aspect of the present invention relates to a doctor blade according to independent claim 9.

[0063] Typically, the section of the edge layer with the higher hardness differs from other areas of the doctor blade in that the material has a different microstructure and / or microstructure created by the laser curing process. In particular, the chemical composition of the material in the section of the edge layer with the higher hardness does not differ significantly or even completely from the composition of the other areas.

[0064] The doctor blade is obtainable in particular by a process according to the invention as described above.

[0065] The section of the surface layer with the higher hardness is obtainable or has been created by irradiating the section with a pulsed laser light beam. In particular, laser light beams such as those described above in connection with the method according to the invention are used.

[0066] A hardness of the section of the surface layer with the higher hardness is 1.1 - 10 times, in particular 1.5 - 5 times, as great as the hardness of the underlying area of ​​the working edge and / or the fastening area.

[0067] In particular, the surface layer with the higher hardness has a layer thickness of 2 - 20 µm, preferably 3 - 10 µm.

[0068] This allows the wear resistance of the working edge of the squeegee to be significantly increased without impairing the mechanical properties of the squeegee.

[0069] According to a particularly preferred embodiment, the surface of the outer edge layer in the section with the higher hardness has periodically arranged depressions and / or elevations. Particularly preferably, the periodically arranged depressions and / or elevations are distributed over the entire surface of the outermost edge layer in the section with the higher hardness.

[0070] In particular, the depressions and / or elevations have a mean spacing (RSm value) of 5 - 100 µm, especially 10 - 50 µm. The mean spacing (RSm value) is determined according to the ISO 4287:2010 standard.

[0071] Particularly preferably, the surface with the periodically distributed depressions and / or elevations has a roughness, expressed as the arithmetic mean deviation (Ra), of 10-500 µm, in particular 150-300 µm. The mean deviation (Ra) is determined according to the ISO 4287:2010 standard.

[0072] According to an advantageous embodiment, the section of the edge layer with the higher hardness and, if present, with the periodically distributed depressions and / or elevations, is coated with an additional coating. The additional coating is constructed and composed, in particular, as explained above in connection with the method according to the invention.

[0073] According to a further and particularly preferred embodiment, the section of the edge layer with the higher hardness and, if present, with the periodically distributed depressions and / or elevations, is free of an additional coating.

[0074] A particular advantage of the combination of surface structuring and surface hardening compared to conventional coating systems for minimizing wear is the following: There is no additional material deposit, as is the case with conventional coatings, which always create an additional layer of material. This allows for very thin lamellae to be produced. This, in turn, results in smaller contact zones, which create less adhesion between the squeegee and cylinder. Thus, in addition to minimizing fluid friction between the squeegee and ink, the adhesion between the squeegee and cylinder is also reduced. At the same time, the hardened surface layer protects against abrasive wear without increasing the contact zone through additional material deposit. This also minimizes shear hardening in the shear gap.

[0075] Further advantageous embodiments and combinations of features of the invention emerge from the following detailed description and the entirety of the patent claims. Short description of the drawings

[0076] The drawings used to explain the embodiment show: Fig. 1 shows a first arrangement for parallel processing of two doctor blades in a side view; Fig. 2 shows the arrangement of Fig. 1 from above; Fig. 3 the first arrangement during the machining process along the line A - A in Fig. 2 ; Fig. 4 a second arrangement for processing a doctor blade wound in the form of a roll in a perspective view; Fig. 5 the spiral course of the working edge of the wound doctor blade from Fig. 4 ; Fig. 6 the top and bottom sides of the doctor blade in the wound roll Fig. 4; Fig. 7 a third arrangement for processing a doctor blade wound on a hollow cylindrical winding core in a perspective view; Fig. 8 the arrangement of Fig. 7 in a sectional view along the line A - A; Fig. 9 the conical spiral shape of the working edge of the doctor blade from Fig. 7 ; Fig. 10 a fourth arrangement for the simultaneous processing of two doctor blades, which are wound spirally into each other in the form of a cylinder via deflection coils in a side view; Fig. 11 the arrangement of Fig. 10 in a plan view along the running direction of one doctor blade; Fig. 12The arrangement of the doctor blades from Fig. 10with oppositely arranged working edges; Fig. 13 a micrograph of the working edge of a blade doctor blade made of carbon steel, machined according to the invention with a pulsed laser; Fig. 14 the surface of the working edge of another blade doctor blade made of carbon steel, machined according to the invention with a pulsed laser, with crater-shaped structures; Fig. 15 the surface of the working edge of another blade doctor blade made of carbon steel, machined according to the invention with a pulsed laser, with scale-like structures; Fig. 16 a micrograph of the working edge of a doctor blade machined with a continuous laser.

[0077] In principle, identical parts in the figures are provided with identical reference symbols. Ways to implement the invention

[0078] Fig. 1 shows a first arrangement 10 for processing doctor blades in a side view. Fig. 2 shows arrangement 10 from above.

[0079] The assembly 10 includes a payoff reel 11 with two spools 11a and 11b. A doctor blade 16a, 16b, e.g., a lamella doctor blade made of carbon steel, is wound on each of the two spools 11a and 11b. For laser hardening of the doctor blades 16a, 16b, the doctor blades are guided parallel to one another through a belt cleaning device 13 and then past a laser processing station 14 to a take-up reel 12. The take-up reel 12 has two spools 12a, 12b for holding the doctor blades 16a, 16b. The laser processing system 14 includes a laser light source 14.1, e.g., a pulsed fiber laser, with a downstream galvanometer scanner, with which the laser beam can be spatially moved.

[0080] During operation, the laser processing system 14 emits a pulsed laser light beam 15, which strikes the working edges 16a.1, 16b.1 of the squeegees 16a, 16b to be processed. The squeegees can be hardened in the area of ​​the working edge 16a.1, 16b.1 and, if necessary, simultaneously structured on the surface.

[0081] Fig. 3 shows the arrangement 10 during the machining process along the line A - A in Fig. 2 . The squeegees 16a, 16b are used to process the underside of the working edges 16a.1, 16b.1 as well as the adjoining end faces.

[0082] Fig. 4 shows a second arrangement 20 for processing a doctor blade 26 wound in the form of a roll 21 in a perspective view.

[0083] The wound doctor blade 21 is rotated around the cylinder axis of the roll 21 for processing and is processed from a direction parallel to the cylinder axis by a laser light beam 25 emerging from the laser processing system 24. The laser processing system 24 includes a pulsed laser light source 24.1 and a movement device 24.2 for displacing the laser light source 24.1 along the diameter of the roll 21.

[0084] Fig. 5 shows the spiral course of the working edge 26.1 of the wound doctor blade 26. The upper and lower sides of the doctor blade 26 are located as in Fig. 6 As shown, they lie directly on top of one another, so that the working edge 26.1 of the doctor blade 26 points upwards. By rotating the doctor blade 26 or the roller 21 and simultaneously moving the laser processing system 24 along the diameter of the roller 21, the working edge 26.1 can be machined along its entire length.

[0085] Fig. 7shows a third arrangement 30 for processing a doctor blade 36 wound on a hollow cylindrical winding core 31 in a perspective view.

[0086] The wound doctor blade 36 is rotated around the cylinder axis of the winding core 31 for processing and is processed from a direction perpendicular to the cylinder axis or the outer surface of the winding core 31 by a laser light beam 35 emerging from a laser processing system 34. The laser processing system 34 includes a pulsed laser light source 34.1 and a movement device 34.2 for displacing the laser light source 34.1 parallel to the rotational axis of the winding core 31.

[0087] The doctor blade 36 is wound such that the working edge 36.1 of the doctor blade 36 forms a conical spiral and is at least partially exposed along its entire wound length from a direction perpendicular to the outer surface of the winding core 31. Fig. 8To clarify the arrangement, shows a section along the line A - A from Fig. 7 The conical spiral shape of the working edge 36.1 is Fig. 9 shown schematically.

[0088] By rotating the winding core 36 and simultaneously moving the laser processing system 34 parallel to the rotation axis of the winding core 31, the working edge 36.1 of the doctor blade 36 can be processed along its entire length on the underside as well as the inclined front side.

[0089] Fig. 10 shows a fourth arrangement 40 for the simultaneous processing of two doctor blades 46a, 46b, which are wound spirally into each other in the form of a cylinder 42 from two separate reels 41a, 41b via deflection reels 47a, 47b. The two doctor blades 46a, 46b are aligned such that the working edges 46a.1, 46b.1 of the two doctor blades face away from each other in the wound state. This is shown in Fig. 12 shown.

[0090] The doctor blades 46a, 46b wound in the shape of the cylinder 42 are rotated around the cylinder axis for processing and are processed from opposite directions by a laser light beam 45a, 45b emerging from a laser processing system 44a, 44b. The laser processing systems 44a, 44b each include a pulsed laser light source and a movement device for displacing the laser light source along a direction parallel to the diameter of the cylinder 21 (indicated by arrows).

[0091] By rotating the cylinder 41 and simultaneously moving the laser processing systems 44a, 44b along the direction parallel to the diameter of the cylinder 21, the working edges 46a.1, 46b.1 of the two doctor blades 46a, 46b can be processed independently of one another along their entire length at the end faces.

[0092] Fig. 13shows a micrograph of the working edge of a carbon steel blade doctor blade machined according to the invention with a pulsed laser. Pulsed laser light with a wavelength of 1,064 nm, a pulse duration of 500 ns, a power of 20 watts, a focus diameter of 30 µm, and a scanning speed of 3,500 mm / s was used for the processing. The working distance between the doctor blade and the laser light source was 176 mm, and the relative speed between the laser light beam and the working edge in the longitudinal direction was 1 m / min.

[0093] As from Fig. 13 As can be seen, the squeegee has a machined underside (in Fig. 13 above) and on the front side a surface layer several micrometers thick, which has a fine-grained structure (bright area in Fig. 13Hardness measurements have shown that the hardness of the surface layer is approximately 900 HV 0.2 (Vickers hardness), which is significantly higher than the underlying areas of the doctor blade's base body (approx. 650 HV 0.2).

[0094] Fig. 14 shows the surface of the working edge of another blade doctor blade made of carbon steel, processed according to the invention with a pulsed laser. Pulsed laser light with a wavelength of 1,064 nm, a pulse duration of 500 ns, a power of 20 watts, a focus diameter of 30 µm, and a scanning speed of 6,000 mm / s was used for processing. The working distance between the doctor blade and the laser light source was 176 mm, and the relative speed between the laser light beam and the working edge in the longitudinal direction was 2 m / min.

[0095] The crater-shaped, periodically distributed depressions and elevations in the surface are clearly visible. The depressions and elevations have a mean spacing (RSm value) according to ISO 4287:2010 of approximately 30 µm, while the roughness, expressed as the arithmetic mean deviation (Ra), is approximately 22 µm according to ISO 4287:2010.

[0096] Fig. 15 shows the surface of the working edge of another carbon steel blade doctor blade machined with a pulsed laser according to the invention. Pulsed laser light with a wavelength of 1,064 nm, a pulse duration of 556 ns, a power of 20 watts, a focus diameter of 30 µm, and a scanning speed of 7,000 mm / s was used for the processing. The working distance between the doctor blade and the laser light source was 176 mm, and the relative speed between the laser light beam and the working edge in the longitudinal direction was 1 m / min.

[0097] The scale-like, periodically distributed depressions and elevations in the surface are clearly visible. The depressions and elevations have a mean spacing (RSm value) according to ISO 4287:2010 of approximately 32 µm, while the roughness, expressed as the arithmetic mean deviation (Ra), is approximately 29 µm according to ISO 4287:2010.

[0098] Fig. 16 shows a micrograph of the working edge of a carbon steel blade doctor blade machined with a continuous laser. Continuous laser light with a power of 60 watts, a focus diameter of 1,500 µm, and a scanning speed of 80 mm / s was used for the machining. Fig. 16 As can be seen, the working edge of the squeegee is hardened over a length of approx. 900 µm (light area in Fig. 16 ), while the fastening area behind it was not hardened.

[0099] Squeegees manufactured using pulsed laser light according to the invention have proven to be extremely durable and of high quality compared to untreated squeegees. In particular, the squeegees allow for extremely precise wiping of printing ink during printing processes, and this is achieved throughout the entire service life of the squeegee.

[0100] Further experiments were carried out with I <reppschabern durchgeführt. Beim I<reppvorgang treten in der Kontaktzone unterschiedliche Verschleissmechanismen auf. Zum einem der Reibungsverschleiss, welcher zwischen Trockenzylinder (Yankee Zylinder) und Kreppschaber entsteht. Zum anderem erzeugt die Papierbahn zusätzlichen Verschleiss, welcher beim Gleiten des Papiers über die Kante des Kreppschabers verursacht wird. Durch das erfindungsgemässe Laserhärten der Spitze der Kreppschaber entsteht eine Randschicht an der Kante des Kreppschabers mit hoher Härte, welche langfristig und effektiv vor Verschleiss schützt, welcher vom Papier verursacht wird. Wird nach dem Härten mit dem Laser zusätzliche eine keramische Verschleissschutzschicht aufgetragen, verfügt der Kreppschaber über einen Verschleissschutz gegen sämtliche Verschleissparameter beim I<reppvorgang.

[0101] The methods and doctor blades described above are to be understood merely as illustrative examples which can be modified within the scope of the invention.

[0102] For example, it is possible to choose the angle of incidence of the laser light beam in the arrangements 10, 20, 30 and 40 differently, e.g. obliquely at an angle of, for example, 60°.

[0103] Likewise, in the arrangement 40, for example, two different doctor blades can be processed and / or the process parameters during laser processing can be set differently for both laser processing systems 44a, 44b.

[0104] Instead of the lamella doctor blades shown, differently shaped doctor blades, scrapers or doctor blades can also be processed using the method according to the invention.

Claims

1. Method for processing a doctor blade (16a, 16b, 26, 36, 46a, 46b), in particular a doctor blade for doctoring off printing ink on a printing cylinder, comprising a flat and elongate base body made of carbon steel with a fastening region and a working edge (16a.1, 16b.1, 26.1, 36.1, 46a.1, 46b.1) formed in a longitudinal direction, wherein a surface layer of the working edge of the doctor blade is hardened with a laser light beam (15, 25, 35, 45a, 45b) at least in a section to be processed, characterized in that the laser light beam is a pulsed laser light beam, preferably with a repetition rate of the laser pulses of 100-500 kHz.

2. Method according to claim 1, wherein the laser light beam is moved continuously over the section to be processed on the working edge during processing, preferably with a relative speed between laser light beam and working edge in the longitudinal direction of 0.5-5 m / min, in particular 0.8-4 m / min.

3. Method according to claim 1 or 2, wherein the pulse energy of the pulsed laser light beam is selected such that hardening of the surface layer is effected locally and at the same time periodically distributed depressions and / or elevations are formed in the surface of the surface layer.

4. Method according to at least one of claims 1-3, wherein a focus diameter of the pulsed laser light beam at the point of impingement on the doctor blade is 1-100 µm, in particular 10-50 µm.

5. Method according to at least one of claims 1-4, wherein the working edge is processed with the laser light beam such that a side opposite a processed side of the working edge remains unprocessed.

6. Method according to at least one of claims 1-5, wherein the doctor blade is continuously unwound from a supply reel during processing, is processed with the laser light on the upper side or on the lower side in the unwound state and is preferably then wound on a separate winding reel.

7. Method according to at least one of claims 1-5, wherein the doctor blade (26) is processed in the roll-wound state, and wherein: a) the doctor blade (26) is wound in a spiral shape and is processed with laser light (25) and present in the form of a cylinder from a direction parallel or obliquely to the cylinder axis, wherein preferably the doctor blade (26) wound in a spiral shape is rotated about the cylinder axis during processing and preferably at the same time the laser beam (25) is moved along a diameter line of the doctor blade (26) wound in a cylindrical shape; or b) two separate doctor blades (46a, 46b) are wound in a spiral shape in opposite directions into one another in the form of a cylinder (42), wherein the two doctor blades (46a, 46b) are aligned such that the working edges (46a.1, 46b.1) of the two separate doctor blades (46a, 46b) face away from one another in the wound state, and are processed with laser light (45a, 45b) from two separate laser light sources from both end sides of the cylinder from a direction parallel or obliquely to the cylinder axis; or c) wherein the doctor blade (36) is wound in a helical shape around the circumferential surface of a cylindrical winding core (31), such that the working edge (36.1) of the doctor blade (36) forms a conical spiral and is exposed along the entire wound length thereof from a direction perpendicular to the circumferential surface of the winding core (31), and is processed with laser light (35) from the direction perpendicular or obliquely to the circumferential surface, and wherein preferably the winding core (31) with the doctor blade wound in a helical shape is rotated about the cylinder axis during processing and in particular at the same time the laser light beam is moved along a direction parallel or obliquely to the cylinder axis.

8. Method according to at least one of claims 1-7, wherein the working edge of the doctor blade is coated with an additional coating after processing with the laser light beam at least in the processed section, wherein the coating is in particular a hard material coating, preferably CrN.

9. Doctor blade (16a, 16b, 26, 36, 46a, 46b), in particular for doctoring off printing ink on a printing cylinder, comprising a flat and elongate base body made of carbon steel with a fastening region and a working edge (16a.1, 16b.1, 26.1, 36.1, 46a.1, 46b.1) formed in a longitudinal direction, wherein the working edge (16a.1, 16b.1, 26.1, 36.1, 46a.1, 46b.1) has, at least in one section, a hardened surface layer obtainable by laser hardening, wherein the working edge (16a.1, 16b.1, 26.1, 36.1, 46a.1, 46b.1) has, in addition to the hardened surface layer, an inner region lying thereunder which has a lower hardness than the surface layer, wherein the section of the surface layer with the higher hardness consists substantially of the same material as the region of the working edge (16a.1, 16b.1, 26.1, 36.1, 46a.1, 46b.1) lying under the hardened surface layer, wherein the hardness of the section of the surface layer with the higher hardness is 1.1-10 times, in particular 1.5-5 times, as great as the hardness of the region of the working edge and / or of the fastening region lying thereunder.

10. Doctor blade according to claim 9, wherein a surface of the outer surface layer has periodically distributed depressions and / or elevations in the section with the higher hardness.

11. Doctor blade according to claim 10, wherein the section of the surface with the periodically distributed depressions and / or elevations has a roughness, expressed as arithmetic mean deviation (Ra), of 10-500 µm, in particular 150-300 µm (ISO 4287:2010) and / or wherein the depressions and / or elevations have a mean distance (RSm value) of 5-100 µm, in particular 10-50 µm (ISO 4287:2010).

12. Doctor blade according to at least one of claims 9-11, wherein at least the section of the surface layer with the higher hardness and, if present, with the periodically distributed depressions and / or elevations, is coated with an additional coating, wherein the coating is in particular a hard material coating, preferably CrN.

13. Doctor blade according to at least one of claims 9-11, wherein the section of the surface layer with the higher hardness and, if present, with the periodically distributed depressions and / or elevations, is free of an additional coating.

Images