EP3936339A1 - Laser machined squeegee - Google Patents

Abstract

In a method for processing a squeegee, in particular a squeegee for squeegeeing off printing ink on a printing cylinder, comprising a flat and elongated base body made of carbon steel with a fastening area and a working edge formed in a longitudinal direction, an edge layer of the working edge of the squeegee is machining section hardened with a laser light beam.

Description

technical field

The invention relates to a method for processing a squeegee, in particular a squeegee for squeegeeing ink off a printing cylinder, comprising a flat and elongated base body made of carbon steel with a fastening area and a working edge formed in a longitudinal direction. The invention further relates to a squeegee with a working edge that is machined at least in one section.

State of the art

Squeegees are used in the printing industry as well as in paper production.

In the printing industry, squeegees are used in particular to scrape off excess printing ink from the surfaces of printing cylinders or printing rollers. The quality of the squeegee has a decisive influence on the printing result, especially in gravure and flexographic printing. Unevenness or irregularities in contact with the printing cylinder working edges of the squeegee lead z. B. to an incomplete stripping of the ink from the webs of the printing cylinder. This can lead to an uncontrolled release of printing ink on the print medium.

During wiping, the working edges of the doctor blade are pressed against the surfaces of the printing cylinders or printing rollers and are moved relative to them. Thus, the working edges, especially in rotary printing presses, are exposed to high mechanical loads on the one hand, which entail corresponding wear and tear - on the other hand, high demands are placed on the working edges of the squeegee, so that precise wiping is ensured over the longest possible period of use. Squeegees are therefore basically consumables, which have to be replaced periodically. It is therefore particularly important to keep the manufacturing costs low and the service life as long as possible while maintaining the same high quality of the squeegee.

Squeegees are usually based on a squeegee body made of steel or plastic with a specially shaped working edge. In order to improve the service life of the squeegee, the hardness of the working edges of the squeegee can be adjusted and/or provided with coatings made of plastics, lacquers, metals and/or hard materials. The structural and material composition of the squeegee has a significant influence on the mechanical and tribological properties.

Such a squeegee is, for example, in the EP 0 911 157 B1 described. This relates to a squeegee for scraping excess printing ink from the surface of a printing form. In order to reduce wear and tear on the surface of the printing form in contact with the squeegee, the lamella and also the area of the rear squeegee part adjoining the lamella are provided with a coating over the entire length of the squeegee, which consists of lubricant or at least has lubricant particles. The coating can include a carrier material in which both lubricant particles and particles of a wear-resistant material are embedded.

the DE 10 2013 011 275 A1 describes a squeegee blade which, on the outer surface in the region of the working edge, has a section facing the printing roller with an ink-friendly surface and an adjoining further section which has an ink-repellent property. With this, the ink spreads better on the more ink-friendly portion, so that the print quality can be increased. The two sections can be made by machining the material of the 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 accepting property.

However, such squeegees are still not completely satisfactory in terms of manufacturing costs and precision when wiping.

In the paper industry, doctor blades are also referred to as doctor blades, doctor blades or coating knives, depending on the application. For example, excess coating color (e.g. pigments, binders, additives, etc.) can be removed from a paper substrate or paper web with a coating knife or doctor blade. As in the printing industry, the life of the doctor blade, doctor blade or coating knife can be improved by modifying the working edges.

the WO 2006/007984 A1 describes, for example, cold-rolled steel strips used in the manufacture of doctor blades, coating blades and creping blades which have improved service life. This is achieved through a special steel composition and the use of a powdered metal process, which results in a composition with a high carbide content. In addition, the working edge can be hardened by a laser beam.

Next describes the WO 92/06796 A1 Squeegee elements, which are designed in particular for engraving paper or cardboard. A special blade design is provided, which allows a greater variation of the contact pressure in order to apply a larger range of line weights. Also mentioned is the additional hardening of the blade in the area of the dosing bevel surface by tempering or laser hardening in order to increase the modulus of elasticity. The hardness on the surface should be less than in the areas below so that the blade can adapt better to the paper or the counter-roller during the grinding-in phase. Also mentioned is the introduction of cross-sectional changes on the blade in the form of grooves, which can also be generated by laser light, among other things.

In the area of doctor blades for the paper industry or for paper manufacture, however, the known systems are not entirely convincing.

There is therefore still a need for improved squeegees for printing technology and also for paper production, which have fewer or none of the disadvantages mentioned above.

Presentation of the invention

The object of the invention is to provide improved methods for the production of doctor blades for printing technology and for paper production, which belong to the technical field mentioned at the outset. In particular, methods are to be created which enable doctor blades to be manufactured as economically as possible. It is also an object of the invention to provide advantageous doctor blades which can be produced as economically as possible and which have the best possible wear resistance for applications in printing technology or in paper production. In particular, the squeegees should at the same time enable printing ink or coating color to be wiped off as precisely as possible.

These objects are solved by the features of independent claims 1 and 10.

In a first aspect, the invention relates to a method for processing a squeegee, comprising a flat and elongated base body made of carbon steel with a fastening area and a working edge formed in a longitudinal direction, a surface layer of the working edge of the squeegee being treated with a laser light beam at least in a section to be processed is hardened.

The term "squeegee" is to be understood broadly in the present case and includes both squeegees for applications in the printing industry and in the paper industry. In particular, the squeegees are pressure squeegees, doctor knives, doctor blades and/or coating knives. In a particularly preferred embodiment, the squeegee is a printing squeegee, which is provided specifically for squeegeeing ink on a printing cylinder.

The expression "squeegee" includes both individual and ready-to-use squeegees cut to length and so-called endless squeegee bands, which in particular can later be cut to length to form a number of individual squeegees. "Endless squeegee strips" in this context mean squeegee strips with a length of at least 5 m, in particular at least 10 m, in particular at least 50 m. For example, the squeegee strip can have a length of 100 m. In a particularly preferred embodiment, the method according to the invention is carried out with endless squeegee belts.

"Carbon steel" is also referred to as carbon steel and is defined as unalloyed quality steel according to the DIN EN 10020:2000 standard. In particular, this type of steel has a carbon content of 0.2 to 0.65% by weight. The proportions of other alloy components are each below a limit specified by the standard. In particular, the carbon steel has the following limit values or maximum proportions: aluminum: 0.30% by weight, boron: 0.0008% by weight, bismuth: 0.10% by weight, cobalt: 0.30% by weight, chromium: 0.30% by weight, Copper: 0.40% by weight, lanthanides (evaluated individually): 0.10% by weight, manganese: 1.65% by weight, molybdenum: 0.08% by weight, niobium: 0.06% by weight, nickel: 0.30% by weight. %, Lead: 0.40% by weight, Selenium: 0.10% by weight, Silicon: 0.60% by weight, Tellurium: 0.10% by weight, Titanium: 0.05% by weight, Vanadium: 0.10% by weight, Tungsten: 0.30% by weight, others (without C; P; S and N) each 0.10% by weight.

In the present case, “hardness” refers to the Vickers hardness determined according to standard DIN EN ISO 6507-1:2018 to -4:2018.

As has been shown, the use of a laser light beam can achieve a temporally and locally controlled energy input into the section of the squeegee made of conventional carbon steel that is to be processed. In contrast to other hardening processes, this enables locally limited hardening. And this without having to use expensive alloy steels. On the one hand, carbon steel doctor blades can be hardened well by laser light beams and, on the other hand, they have excellent mechanical properties for applications in printing technology and papermaking.

Hardening with a laser light beam makes it possible, in particular, to leave the basic body of the squeegee unchanged and only to process the working edge at the desired points. The section of the squeegee to be processed can be hardened from the edge area down to the deeper areas below the surface. Depending on the process parameters and structure of the squeegee, only the edge area can be hardened or the areas of the squeegee underneath are also hardened. This allows the mechanical properties of the squeegee to be adjusted and controlled in a targeted manner.

During the machining process, due to the targeted machining with laser light beams, the energy input can be controlled in such a way that, despite the hardening, undesired deformations of the squeegee are prevented during the machining or the hardening process. This is one of the great advantages of the present invention. Accordingly, the squeegees also have clearly defined working edges after the processing operation.

The process is also very flexible, since it can be used for different squeegee types or squeegee geometries by adjusting the process parameters. Due to the possibility of processing endless squeegee strips, the process also allows very economical processing of the squeegee, since the squeegee can, for example, be hardened in a further process step directly after production.

The laser light beam is particularly preferably moved continuously over the section to be machined on the working edge during the machining.

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

The movement of the laser light beam over the section to be processed can in principle be (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 squeegee and laser beam can be achieved.

As has been shown, the continuous movement of the laser light beam over the section to be machined on the working edge can result in a particularly uniform input of energy into the section of the squeegee to be machined. At the same time, due to the continuous relative movement, a stable balance between energy input and heat dissipation can be achieved, for example via the non-processed areas of the squeegee, via heat radiation and/or via additional cooling devices. This can also prevent undesired deformations of the squeegee from occurring during processing or the hardening process.

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

A relative speed between the laser light beam and the working edge in the longitudinal direction during processing is preferably 0.5-5 m/min, in particular 0.8-4 m/min. This enables fast but reliable processing of the working edge.

A power of the laser light beam is preferably 5-50 W, in particular 10-30 W. This allows the materials typically used for doctor blades, such as steel, to be hardened well. For other materials or special squeegees, however, lower or higher outputs can also be suitable.

The light of the laser light beam is particularly preferably UV light, visible light or infrared radiation. A wavelength of the light is, for example, in the range of 150 nm-3 μm, preferably 400 nm-2.5 μm, in particular 500 nm-1.5 μm. In the case of short wavelengths in particular, the surface of the working edge can be additionally structured during processing by ablation. Longer wavelengths are particularly suitable in the event that no additional structuring or ablation-free structuring is desired.

According to one possible embodiment, the laser light beam is a continuous wave laser light beam. A continuous-wave laser light beam, also called "continuous-wave laser light beam", consists of light waves with a constant intensity over time. A diode laser or a fiber laser can be used, for example.

With a continuous wave laser light beam, larger sections of the working edge in particular can be evenly hardened in a short time. Several squeegees can also be hardened in parallel if the focus of the laser light beam is set large enough.

In an advantageous embodiment, the focus of the continuous wave laser light beam on the squeegee is, for example, 1-10 mm×1-10 mm, in particular 2-5 mm×5-8 mm.

According to a particularly preferred embodiment, the laser light beam is a pulsed light laser beam. A pulsed light laser beam has a pulsating intensity of light waves.

As it has surprisingly turned out, the use of pulsed light laser beams in the present case offers several advantages. In this way, the energy input into the section to be processed can be controlled more precisely. In this way, for example, the surface layer can be selectively hardened while the areas underneath retain their original hardness. It is also possible, for example, to develop a gradual decrease in hardness from the edge area in the direction of the areas below. This without causing a significant deformation of the squeegee.

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, in particular reduced. As has been shown, this, in combination with the increased hardness, leads to a strong increase in the wear resistance of the squeegee with improved scraping properties at the same time.

Without being bound to 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 assumed to be that the structuring of the surface results in a reduction in surface tension, which in turn should lead to the molecules of the printing ink interacting more strongly with each other than with the working edge of the squeegee. As a result, there appears to be less liquid friction between the squeegee and the printing ink.

It was also possible to minimize negative application-related effects that occur between the squeegee and the printing ink during the printing process. Specifically could all application-related errors are minimized, which are caused by the Barus effect and the Coanda effect.

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

The method is particularly preferably carried out in such a way that the laser light beam scans the working edge of the squeegee 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-deflectors for deflecting and focusing laser beams in one dimension, or by XY deflectors for deflecting and focusing laser beams in two dimensions. For example, so-called galvanometer scanners with mirrors are suitable.

A scanning speed of the laser light beam is preferably 1,000-10,000 mm/s.

A repetition rate of the laser pulses is, for example, 100-500 kHz.

A focus diameter of the pulsed laser light beam at the point of impact on the squeegee is advantageously 1-100 μm, in particular 10-50 μm. Relatively fine structures can thus also be produced in the surfaces of the working edge and the hardening of the working edge can be spatially defined very precisely.

The method is preferably controlled by a control unit, the control unit coordinating and controlling 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.

According to a preferred embodiment, the working edge of the squeegee 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 squeegee is processed on a first side and possibly on the front side, but not on the second side of the working edge, which is opposite the first side.

As has been shown, the side of the working edge which was first structured and/or hardened with the laser can at least partially lose the previously gained hardness during the processing of the opposite side due to the renewed input of thermal energy into the substrate.

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

Deformations when both sides of the working edge are processed simultaneously are likely to be due to the fact that the simultaneously occurring energy input of thermal energy into the substrate on both sides is twice as high as the comparable time-staggered input of energy into the substrate.

However, empirically obtained data show that one-sided surface structuring and/or hardening of the surface layer of the working edge is completely sufficient with regard to wear resistance and stripping behavior if the side of the working edge facing the printing cylinder is processed according to the invention. No disadvantages compared to a squeegee with treatment on both sides could be determined. On the other hand, the processing of the squeegee is significantly simplified and more economical.

According to advantageous methods, the squeegee is continuously unwound from a supply reel during processing, processed in the unwound state with the laser light beam on the upper side or on the underside and then preferably on a separate reel is wound up. As a result, endless squeegee strips that have already been wound up can 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.

It can be advantageous to unwind two doctor blades parallel to each other from a storage reel, to guide them parallel to each other in the unwound state and to process them with the laser light beam on the top or bottom and then preferably to wind them up on a separate take-up reel. The squeegees are preferably guided side by side in such a way that the working edges to be processed face each other. This has the advantage that the laser light beam can process the two squeegees simultaneously, as a result of which the throughput in particular can be increased. In principle, the two squeegees can be processed with identical or different parameters.

In a further and particularly advantageous embodiment, the squeegee is processed in the state in which it is wound up in the form of a roll. It is possible, for example, to wind the squeegee onto a cylindrical winding body.

Processing in a state wound up in the form of a roll minimizes the space requirement on the one hand. On the other hand, the squeegee forms a compact body made up of layers lying one on top of the other. This makes it possible to effectively disperse and dissipate the heat generated during machining, reducing or preventing the problem of deformation.

The squeegee is preferably wound up in a spiral shape and, in the present case in the form of a cylinder, is processed with the laser light beam from a direction parallel or at an angle to the cylinder axis. In this way, the squeegee can be processed in particular 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 at the same time.

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

According to a further advantageous embodiment, two separate squeegees are spirally wound into one another in the form of a cylinder in opposite directions. The two squeegees are preferably aligned in such a way that the working edges of the two separate squeegees face away from one another in the wound-up state. The working edge of one squeegee is then part of one end face of the cylinder, while the working edge of the second squeegee is part of the opposite end face of the cylinder.

The two end faces of the cylinder are preferably processed from a direction parallel or at an angle to the cylinder axis with laser light beams from two separate laser light sources. This means that both squeegees can be processed at the same time. Here again it is possible to carry out the processing of the squeegee with identical or different parameters.

A further and particularly advantageous embodiment provides that the squeegee is wound helically around the lateral surface of a cylindrical winding core, so that the working edge of the squeegee forms a conical spiral and is at least partially exposed along its entire wound length from a direction perpendicular to the lateral surface of the winding core. Depending on the gradient of the conical spiral formed, a larger or smaller part of the working edge is exposed.

The squeegee is preferably processed with laser light from a direction perpendicular or at an angle to the lateral surface. The working edge can thus be processed on the face side and/or in the area of the underside or top of the squeegee.

In particular, the winding core with the helically wound squeegee 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 at an angle to the cylinder axis. This allows the laser light beam to work the working edge of the coiled squeegee along the entire longitudinal length.

If there is a winding core, in one possible embodiment this is cooled during processing with the laser light beam. This allows the heat dissipation to be additionally increased and controlled. However, cooling is not mandatory.

Furthermore, it can be preferred if the working edge of the squeegee is covered with an additional coating after processing with the laser light beam, at least in the processed section. For example, this is a wear-reducing and/or a friction-reducing coating. The coating can be, for example, a metal coating, a hard coating, a ceramic coating or a polymer coating. With such coatings, the squeegee can be further customized for specific applications. As has surprisingly been shown, a squeegee structured on the surface according to the invention can form an adhesive layer and/or intermediate layer, so that the additional coating adheres better.

A second aspect of the present invention relates to a squeegee, in particular for squeegeeing off printing ink on a printing cylinder, comprising a flat and elongated base body made of carbon steel with a fastening area and a working edge formed in a longitudinal direction, the working edge being at least in a section a laser hardening obtainable , Has hardened surface layer.

In particular, the hardened surface layer has a higher hardness than the fastening area of the squeegee.

According to a particularly preferred embodiment, the working edge has, in addition to the hardened surface layer, an underlying inner region which has a lower hardness than the surface layer. In this embodiment, only the surface layer of the working edge is hardened.

The section of the edge layer with the greater hardness consists essentially of the same material as the other areas of the base body of the doctor blade, in particular the fastening area and/or the areas of the working edge lying under the hardened edge layer. Typically, the higher hardness portion of the surface layer differs from other areas in that the material has a different Has microstructure and / or microstructure, which was generated by the laser hardening process. In particular, the chemical composition of the material in the section of the surface layer with the higher hardness does not differ significantly or not from the composition of the other areas.

The doctor blade can be obtained in particular by a method according to the invention as described above.

The section of the surface layer with the greater hardness can advantageously be obtained or produced by laser hardening or by irradiating the section with a laser light beam, in particular a pulsed laser light beam. In particular, laser light beams are used here, as described above in connection with the method according to the invention.

A hardness of the section of the surface layer with the higher hardness is preferably 1.1-10 times, in particular 1.5-5 times, as great as the hardness of the area of the working edge and/or the fastening area lying underneath.

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

The wear resistance of the working edge of the squeegee can thus be greatly increased without impairing the mechanical properties of the squeegee.

According to a particularly preferred embodiment, the surface of the outer edge layer has periodically arranged indentations and/or elevations in the section with the greater hardness. The periodically arranged indentations and/or elevations are particularly preferably distributed over the entire surface of the outermost surface layer in the section with the greater hardness.

In particular, the depressions and/or elevations have an average spacing (RSm value) of 5-100 μm, in particular 10-50 μm. The average distance (RSm value) is determined according to the ISO 4287:2010 standard.

The surface with the periodically distributed depressions and/or elevations particularly preferably 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.

According to an advantageous embodiment, the section of the surface layer with the greater hardness and, if present, with the periodically distributed indentations and/or elevations is covered 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.

According to a further and particularly preferred embodiment, the section of the surface layer with the greater hardness and, if present, with the periodically distributed indentations and/or elevations is free of an additional coating.

A particular advantage of the combination of surface structuring and edge layer hardening compared to conventional layer systems for minimizing wear is as follows: There is no additional material application, as is the case with conventional coatings, which always produce an additional material application. This means that very thin lamellae can be produced. This in turn results in smaller contact zones, which produce less adhesion between doctor blade and cylinder. Thus, in addition to minimizing fluid friction between the squeegee and ink, adhesion between the squeegee and cylinder is also reduced. At the same time, the hardened surface layer protects against abrasive wear without enlarging the contact zone through additional material application. This also results in a minimization of shear thickening in the shearing gap.

Further advantageous embodiments and combinations of features of the invention result from the following detailed description and the entirety of the patent claims.

Brief description of the drawings

Fig. 1

eine erste Anordnung zum parallelen Bearbeiten von zwei Rakeln in einer Seitenansicht;

Fig. 2

die Anordnung aus Fig. 1 von oben;

Fig. 3

die erste Anordnung während dem Bearbeitungsvorgang entlang der Linie A - A in Fig. 2;

Fig. 4

eine zweite Anordnung zum Bearbeiten einer in Form einer Rolle aufgewickelten Rakel in einer perspektivischen Ansicht;

Fig. 5

den spiralförmigen Verlauf der Arbeitskante der aufgewickelten Rakel aus Fig. 4;

Fig. 6

die aufeinanderliegenden Ober- und -Unterseiten der Rakel in der aufgewickelten Rolle aus Fig. 4;

Fig. 7

eine dritte Anordnung zum Bearbeiten einer auf einem hohlzylindrischen Wickelkern aufgewickelten Rakel in einer perspektivischen Ansicht;

Fig. 8

die Anordnung aus Fig. 7 in einer Schnittdarstellung entlang der Linie A - A;

Fig. 9

der konisch spiralförmige Verlauf der Arbeitskante der Rakel aus Fig. 7;

Fig. 10

eine vierte Anordnung zur gleichzeitigen Bearbeitung von zwei Rakeln, welche von zwei separaten Spulen über Umlenkspulen spiralförmig in Form eines Zylinders gegenläufig ineinander aufgewickelt werden in einer Seitenansicht;

Fig. 11

die Anordnung aus Fig. 10 in einer Aufsicht entlang der Laufrichtung der einen Rakel;

Fig. 12

Die Anordnung der Rakel aus Fig. 10 mit entgegen gesetzt angeordneten Arbeitskanten;

Fig. 13

ein Schliffbild der Arbeitskante einer erfindungsgemäss mit einem gepulsten Laser bearbeiteten Lamellenrakel aus Kohlenstoffstahl;

Fig. 14

die Oberfläche der Arbeitskante einer weiteren erfindungsgemäss mit einem gepulsten Laser bearbeiteten Lamellenrakel aus Kohlenstoffstahl mit kraterförmigen Strukturen;

Fig. 15

die Oberfläche der Arbeitskante einer weiteren erfindungsgemäss mit einem gepulsten Laser bearbeiteten Lamellenrakel aus Kohlenstoffstahl mit schuppenartigen Strukturen;

Fig. 16

ein Schliffbild der Arbeitskante einer erfindungsgemäss mit einem kontinuierlichen Laser bearbeiteten Rakel.

The drawings used to explain the embodiment show:

1

a first arrangement for parallel processing of two doctor blades in a side view;

2

the arrangement 1 from above;

3

the first arrangement during the machining process along the line A - A in 2 ;

4

a second arrangement for processing a squeegee wound up in the form of a roll in a perspective view;

figure 5

the spiral course of the working edge of the wound squeegee 4 ;

6

the mating top and bottom sides of the squeegee in the wound roll 4 ;

7

a perspective view of a third arrangement for processing a squeegee wound on a hollow-cylindrical winding core;

8

the arrangement 7 in a sectional view along the line A - A;

9

the conical spiral shape of the working edge of the squeegee 7 ;

10

a fourth arrangement for the simultaneous processing of two squeegees, which are spirally wound into one another in opposite directions from two separate coils via deflection coils in the form of a cylinder, in a side view;

11

the arrangement 10 in a top view along the running direction of a doctor blade;

12

The arrangement of the squeegee 10 with opposed working edges;

13

a micrograph of the working edge of a bladed doctor blade made of carbon steel processed according to the invention with a pulsed laser;

14

the surface of the working edge of a further bladed doctor blade made of carbon steel with crater-shaped structures and machined according to the invention with a pulsed laser;

15

the surface of the working edge of another lamella doctor blade made of carbon steel with scale-like structures, machined according to the invention with a pulsed laser;

16

a micrograph of the working edge of a squeegee processed according to the invention with a continuous laser.

In principle, the same parts are provided with the same reference symbols in the figures.

Ways to carry out the invention

1 shows a first arrangement 10 for processing doctor blades in a side view. 2 shows the assembly 10 from above.

The assembly 10 includes a decoiler 11 having two spools 11a and 11b. A squeegee 16a, 16b, e.g. a lamellar squeegee made of carbon steel, is wound on each of the two coils 11a and 11b. For laser hardening of the squeegees 16a, 16b, the squeegees are guided parallel to one another through a strip cleaning device 13 and then past a laser processing station 14 to a take-up reel 12. The take-up reel 12 has two coils 12a, 12b for receiving the doctor blade 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 moved spatially.

During operation, the laser processing system 14 emits a laser light beam 15, in particular a pulsed laser light beam, which impinges on the working edges 16a.1, 16b.1 of the squeegee 16a, 16b to be processed. The squeegee in the area the working edge 16a.1, 16b.1 hardened and, if necessary, structured at the same time on the surface.

3 shows the arrangement 10 during the machining process along the line AA in 2 . The squeegees 16a, 16b are processed on the underside of the working edges 16a.1, 16b.1 and on the adjoining end faces.

4 shows a second arrangement 20 for processing a squeegee 26 wound up in the form of a roll 21 in a perspective view.

The wound squeegee 21 is rotated about the cylinder axis of the roller 21 for processing and 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 laser light source 24.1, e.g. a pulsed laser light source, and a moving device 24.2 for moving the laser light source 24.1 along the diameter of the roller 21.

figure 5 shows the spiral course of the working edge 26.1 of the wound squeegee 26. The upper and lower sides of the squeegee 26 are as in FIG 6 shown directly on top of each other, so that the working edge 26.1 of the squeegee 26 points upwards. By rotating the squeegee 26 or the roller 21 and at the same time moving the laser processing system 24 along the diameter of the roller 21, the working edge 26.1 can be processed on the end face along its entire length.

7 shows a third arrangement 30 for processing a squeegee 36 wound on a hollow-cylindrical winding core 31 in a perspective view.

For processing, the wound doctor blade 36 is rotated about the cylinder axis of the winding core 31 and processed from a direction perpendicular to the cylinder axis or the lateral 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 laser light source 34.1, e.g. a pulsed laser light source, and a movement device 34.2 for moving the laser light source 34.1 parallel to the axis of rotation of the winding core 31.

The squeegee 36 is wound up in such a way that the working edge 36.1 of the squeegee 36 forms a conical spiral and is at least partially exposed along its entire wound up length from a direction perpendicular to the lateral surface of the winding core 31. 8 shows a section along the line AA to clarify the arrangement 7 . The conical spiral shape of the working edge 36.1 is in 9 shown schematically.

By rotating the winding core 36 and at the same time moving the laser processing system 34 parallel to the axis of rotation of the winding core 31, the working edge 36.1 of the squeegee 36 can be processed along its entire length on the underside and the sloping front side.

10 shows a fourth arrangement 40 for the simultaneous processing of two squeegees 46a, 46b, which are spirally wound into one another in opposite directions from two separate coils 41a, 41b via deflection coils 47a, 47b in the form of a cylinder 42. The two squeegees 46a, 46b are aligned in such a way that the working edges 46a.1, 46b.1 of the two squeegees face away from one another in the wound-up state. this is in 12 shown.

The squeegees 46a, 46b wound up in the form of the cylinder 42 are rotated about the cylinder axis for processing and 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 laser light source, e.g., a pulsed laser light source, and a moving device for displacing the laser light source along a direction parallel to the diameter of the cylinder 21 (indicated by arrows).

By rotating the cylinder 41 and at the same time 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 on the end faces will.

13 shows a micrograph of the working edge of a lamella doctor blade made of carbon steel processed according to the invention with a pulsed laser. For editing was 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. The working distance between the squeegee 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.

How out 13 As can be seen, the squeegee has on the machined underside (in 13 above) and on the front side via a surface layer several micrometers thick, which has a fine-grained structure (light area in 13 ). Hardness measurements have shown that the hardness of the surface layer is approx. 900 HV 0.2 (Vickers hardness) and thus significantly higher than the underlying areas of the base body of the squeegee (approx. 650 HV 0.2).

14 shows the surface of the working edge of another lamella 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 squeegee 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.

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

15 shows the surface of the working edge of another lamella 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 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 processing. The working distance between squeegee 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.

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

16 shows a micrograph of the working edge of a lamella doctor blade made of carbon steel processed according to the invention 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 processing. How out 16 As can be seen, the working edge of the squeegee has hardened over a length of approx. 900 µm (light area in 16 ), while the fastening area behind it has not been hardened.

Squeegees produced according to the invention, in particular those produced with pulsed laser light, have proven to be extremely durable and of high quality compared to untreated squeegees. In particular, the squeegees allow extremely precise stripping of printing ink in printing processes. This during the entire service life of the squeegee.

Tests were also carried out with crepe doctors. Different wear mechanisms occur in the contact zone during the creping process. Firstly, the frictional wear that occurs between the drying cylinder (Yankee cylinder) and the crepe doctor. On the other hand, the paper web generates additional wear, which is caused when the paper slides over the edge of the crepe doctor. The laser hardening of the tip of the creping blade according to the invention creates a highly hard surface layer on the edge of the creping blade, which provides long-term and effective protection against wear caused by the paper. If an additional ceramic wear protection layer is applied after hardening with the laser, the creping doctor has wear protection against all wear parameters during the creping process.

The methods and squeegees described above are only to be understood as illustrative examples which can be modified within the scope of the invention.

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

Likewise, with the arrangement 40, for example, two different squeegees can be processed and/or the process parameters during the laser processing are set differently for the two laser processing systems 44a, 44b.

Instead of the lamellar squeegee shown, other shaped squeegees, scrapers or doctor blades can also be processed using the method according to the invention.

Claims (16)

Method for processing a squeegee, in particular a squeegee for squeegeeing off printing ink on a printing cylinder, comprising a flat and elongated base body made of carbon steel with a fastening area and a working edge formed in a longitudinal direction, with an outer layer of the working edge of the squeegee at least in a section to be processed hardened with a laser light beam. Method according to claim 1, wherein the laser light beam is continuously moved during processing over the section to be processed on the working edge, preferably at a relative speed between the laser light beam and the working edge in the longitudinal direction of 0.5 - 5 m/min, in particular 0.8 - 4 m/min. Method according to at least one of claims 1 - 2, wherein the laser light beam is a pulsed light laser beam, preferably with a repetition rate of the laser pulses of 100 - 500 kHz. Method according to claim 3, wherein the pulse energy of the pulsed laser light beam is selected such that the surface layer is hardened locally and at the same time periodically distributed depressions and/or elevations are formed in the surface of the surface layer. Method according to at least one of claims 3 - 4, wherein a focus diameter of the pulsed laser light beam at the point of impact on the squeegee is 1 - 100 µm, in particular 10 - 50 µm. Method according to at least one of claims 1 - 5, wherein the working edge is processed with the laser light beam in such a way that a side opposite a processed side of the working edge remains unprocessed. Method according to at least one of Claims 1 - 6, in which the doctor blade is continuously unwound from a supply reel during processing, in unwound Condition is processed with the laser light on the top or bottom and is then preferably wound up on a separate reel. Method according to at least one of claims 1 - 6, wherein the squeegee is processed in the state wound up in the form of a roll, and wherein: a) the squeegee is wound up spirally and, in the form of a cylinder, is processed with laser light from a direction parallel or at an angle to the cylinder axis, with the squeegee wound up in a spiral shape preferably being rotated about the cylinder axis during processing and at the same time preferably the laser beam being along a diameter line of the cylindrically wound up squeegee squeegee is moved; or b) two separate squeegees are spirally wound into each other in the form of a cylinder in opposite directions, with the two squeegees being aligned in such a way that the working edges of the two separate squeegees face away from each other when wound up, and from both end faces of the cylinder from a direction parallel or oblique to cylinder axis are processed with laser light from two separate laser light sources; or c) the doctor blade being helically wound around the lateral surface of a cylindrical mandrel such that the working edge of the doctor blade forms a conical spiral and is exposed along its entire wound length from a direction perpendicular to the mantle surface of the mandrel and from the direction perpendicular or oblique to the mantle surface is processed with laser light and wherein the winding core with the helically wound squeegee is preferably 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 at an angle to the cylinder axis. Method according to at least one of claims 1 - 8, 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, which is in particular a hard material coating, preferably CrN. Squeegee, in particular for scraping off printing ink on a printing cylinder, comprising a flat and elongated base body made of carbon steel with a fastening area and a working edge formed in a longitudinal direction, the working edge having a hardened surface layer obtainable by laser hardening in at least one section. 11. The squeegee of claim 10, wherein the working edge has, in addition to the hardened skin, an underlying interior region that has a lower hardness than the skin, the higher hardness portion of the skin being of substantially the same material as that underlying the hardened skin The area of the working edge consists, in particular the surface layer with the higher hardness having a layer thickness of 2-20 μm, preferably 3-10 μm. Squeegee according to at least one of claims 10 - 11, 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 underlying area of the working edge and/or the fastening area. Squeegee according to at least one of claims 10 - 12, wherein a surface of the outer edge layer has periodically distributed indentations and/or elevations in the section with the greater hardness. Squeegee according to claim 13, wherein the section of 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 (ISO 4287:2010) and /or wherein the depressions and/or elevations have an average distance (RSm value) of 5 - 100 µm, in particular 10 - 50 µm (ISO 4287:2010). Squeegee according to at least one of claims 10 - 14, wherein at least the section of the surface layer with the higher hardness and, if present, with the periodically distributed depressions and/or elevations, with an additional coating is coated, which is in particular a hard material coating, preferably CrN. Squeegee according to at least one of claims 10 - 14, wherein 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.

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