Surface treatment device in a sheet processing machine and a method for this

Abstract

Surface treatment device in a sheet processing machine with a gap extending transversely to a sheet conveying direction (BFR), which is arranged at a distance from the sheet transport path and with means for applying a vacuum that smooths the sheet (5) conveyed past the gap against the gap, where powder nozzles (4.4) for powdering the arc (5) are assigned to the gap, wherein the gap is assigned suction nozzles (4.6) as a bow smoother (4) for generating a vacuum and / or for extracting the powder, wherein the powder nozzles (4.4) are designed as impact nozzles which spray the powder against at least one impact surface and wherein the sheet smoother (4) is arranged in recesses of sheet guide plates below the sheet transport path in the delivery (1) of a sheet-fed printing press.

Description

[0001] The invention relates to a surface treatment device in a sheet processing machine and a method for this.

[0002] From DE 41 09 876 A1 a sheet smoother in the delivery of printing presses is known, in which the sheets to be laid down are conveyed over two support bodies arranged at a distance from each other, which are arranged transversely to the sheet travel direction and over the entire sheet width and are drawn into the smoothing gap by means of suction air.

[0003] From DE 198 36 022 A1, a device for dusting printed sheets of paper or the like is known, in which the sheet is electrostatically charged before the powder dusting device. The powder dusting device is intended to be arranged in front of a sheet unwinder. A disadvantage of this solution is that the powder dusting device must be at a large distance from the paper sheet to allow the gripper to pass by. This leads to powder contamination of the delivery.

[0004] From DE 10 2008 009 156 A1, an arrangement for dissipating electrostatic charges from a printing substrate is known. It is known from this that sheets on a sheet unwinder of a printing press can become so strongly charged that a subsequent powder application is impaired.

[0005] From DE 103 08 406 A1, a machine for processing flat substrates is known, comprising a processing station that can be operated as a die-cutting unit. In a first installation position, a suction device can be installed in a guide surface of a guide device for extracting the offcuts during die-cutting operation. In a second installation position, a pneumatic sheet flattening device is provided at this location. If, during front and back printing without die-cutting, neither the suction device nor the sheet flattening device is to be used, the gap in the guide device can be closed.

[0006] From US 4,002,047 it is known to switch the vacuum supply of a single sheet smoother arranged below the sheet conveying path so that the sheets can be powdered.

[0007] In printing presses with a floating sheet guide, the stability of the sheet travel depends heavily on the homogeneity of the sheet guide. Gaps, bumps, and breaks in the sheet guide lead to impaired sheet travel (flutter). Nevertheless, especially in perfecting mode, it can be advantageous to powder not only the top but also the (printed) underside of the sheet, although this involves breaking up the homogeneous sheet guide.

[0008] The invention is therefore based on the objective of creating a method and a surface treatment device in a sheet-processing machine which improves sheet powdering while maintaining consistently good sheet guidance.

[0009] According to the invention, the problem is solved by a device having the features of claim 1 and a method having the features of claim 12.

[0010] The invention has the advantage of creating installation space in the display and improving the application of powder to the underside of the sheet.

[0011] One embodiment of the invention has the advantage that the powder application can take place very close to the sheet without disrupting sheet transport along the sheet guide elements. This enables more efficient sheet transport in the delivery of a printing press. The sheet smoother creates a discontinuity in the sheet guide that is always present and cannot be avoided. The invention is based on the idea of ​​utilizing this discontinuity for the arrangement of a powdering device, the placement of which elsewhere would create another undesirable discontinuity. In principle, the invention can also be used on other machines, such as after a cross cutter of a rotary printing press.

[0012] Additionally, the sheets can be powdered from above, thus coating both sides with powder. In a further development of the invention, the powdering device, located above the sheet transport path, is positioned opposite the sheet smoother.

[0013] In a preferred embodiment of the invention, the powder nozzles are designed as impact nozzles that spray the powder against a flank of the sheet smoother, which is configured as an impact surface. For this purpose, the impact nozzles are arranged at a defined angle to the flank. The powder flow directed against the impact surface ensures a uniform powder distribution, which forms a mixing flow with the air cushion flow created by the upstream sheet guide element. Advantageously, the air parameters so important for sheet movement, such as pressure and velocity, are kept essentially the same before and after the smoothing gap.

[0014] The invention will now be explained by way of example. The accompanying drawings schematically illustrate the following: Fig. 1: Delivery of a sheet-fed printing press with a sheet smoother arranged below the sheet transport path; Fig. 2: Arc smoother with nozzles arranged in the gap base; Fig. 3: Arc smoother with nozzles in the gap base and on the sides; Fig. 4: Preferred further development of the arc smoother in cross-section with powder nozzles designed as impact nozzles.

[0015] The Fig. Figure 1 shows a section of the delivery unit 1 of a sheetfed offset rotary printing press. The delivery unit 1 comprises a sheet conveyor system 3 designed as a chain conveyor system, which takes the printed sheets 5 from a sheet guide cylinder 2 and conveys them to the delivery stack 6. For sheet transport, the chain conveyor system 3 has rotating gripper carriages that fix the sheets 5 at the leading edge and guide them along a sheet conveyor path in the sheet conveying direction BFR to the delivery stack 6. The sheet guide cylinder 2 can be a printing cylinder of a final printing, coating, or other finishing unit, or a transfer drum, etc. The printing press is equipped with a perfecting unit for changing the operating mode from single-sided printing to double-sided printing. The perfecting unit can be designed as a single-drum or a three-drum perfecting unit.In single-sided printing mode, the sheet is printed on one side, while in double-sided printing, the other side of the sheet is processed after the turning device.

[0016] On the sheet conveying path from the sheet guide cylinder 2 to the delivery stack 6, the sheets 5 are guided by sheet guide elements (not shown), for example, sheet guide plates, with an air cushion preferably formed between the sheet 5 and the sheet guide plates. A gap is arranged below the sheet conveying path in a break in the sheet guide plates, extending over the entire maximum sheet width to be processed. The gap is designed as a sheet smoother 4 and, in the front-printing mode, is operated with a vacuum to smooth the sheets 5. In the front-printing mode, the sheet smoother 4 is generally deactivated to prevent damage to the underside of the sheets.

[0017] The Fig. Figure 2 shows a sheet smoother 4 in a first embodiment of the invention, which is swept over by sheets 5 (not shown) in the sheet conveying direction BFR. Viewed in the sheet conveying direction BFR, the sheet smoother 4 comprises a downward-sloping flank 4.1, a gap base 4.2, and a rising flank 4.3. The gap base 4.2 is thus located below and spaced apart from the sheet conveying plane. The downward-sloping flank 4.1 and the rising flank 4.3 are arranged in a V-shape, preferably with an optimized radius of curvature.

[0018] The powder nozzles 4.4 required for powdering the underside of the bow are arranged in the gap base 4.2, which are in Fig. 2, for example, are shown in several groups of three. Only one of the identical powder nozzles 4.4 is designated here. Between the groups of powder nozzles 4.4, further support nozzles 4.5 are arranged, which are connected to a compressed air source. By means of the support nozzles 4.5, an adjustable overpressure can be generated in the gap of the sheet smoother 4, guiding the sheet 5. When overpressure is applied, no sheet smoothing by the sheet smoother 4 takes place. In the area of ​​the gap base 4.2, suction nozzles 4.6 are also arranged, which can generate a negative pressure in the gap and are also used for powder extraction. The suction capacity of the suction nozzles 4.6 is preferably adjustable. Powder extraction is necessary to prevent clogging of the device. If a negative pressure is applied in the gap of the sheet smoother 4 by the suction nozzles 4.6, the sheet 5 guided over the sheet smoother 4 is drawn in and smoothed.However, it is also possible to generate the negative and positive pressure via common nozzles in the sheet smoother 4 by means of appropriately connected suction or compressed air sources.

[0019] The Fig. Figure 3 shows a second embodiment of the invention, a sheet smoother 4, which is swept over by sheets 5 (not shown) in the sheet conveying direction BFR. The powder nozzles 4.4 and the suction nozzles 4.6 arranged in the gap base 4.2 are visible. In contrast to the sheet smoother 4 according to Fig. Here, the support nozzles 4.5 are arranged on the falling flank 4.1 and the rising flank 4.3. The nozzles can, of course, also be arranged on only one flank and / or have flow-optimized nozzle exit angles relative to the arc conveying direction (BFR). It is also possible to arrange the powder nozzles 4.4 alternatively or additionally on one or both flanks of the arc smoother 4. The flanks of the arc smoother 4 can also be formed by tubular elements with a gap between them.

[0020] In a further development of the invention, the powder nozzles 4.4 are mounted in such a way that their distance to the sheet conveying plane can be changed. Advantageously, this allows the distance of the powder nozzles 4.4 to the underside of the sheet to be minimized when the sheet 5 is fed past the sheet smoother 4 in the operating mode of perfecting without sheet flattening. It is also provided that the powdering can be adjusted to the currently processed sheet format by switching off individual powder nozzles 4.4, thereby reducing powder consumption and powder contamination in the delivery 1.

[0021] In a further embodiment of the invention, it is provided that the powder is not applied to the underside of the sheet in a stream or as a curtain, but rather that the space enclosed by the sheet smoother 4 and sheet 5 is enriched with a powder-air mixture, from which powder particles are deposited on the underside of the sheet 5.

[0022] The Fig.Figure 4 shows a cross-sectional view of a sheet smoother 4 in a preferred embodiment of the invention. Here, the downward slope 4.1 and the upward slope 4.3 of the sheet smoother 4 are arranged at different angles. The powder nozzles 4.4 are designed as impact nozzles located in the downward slope 4.1 of the sheet smoother 4. These impact nozzles spray the powder in the sheet conveying direction BFR at a defined angle against the upward slope 4.3 of the sheet smoother 4, which is designed as an impact surface, thereby producing a uniform powder distribution within the sheet smoother 4. A resulting fanned powder flow 7.2 within the sheet smoother 4 forms a mixing flow 7.3 with the air cushion flow 7.1 generated between the upstream sheet guide plate and the underside of the sheet. By utilizing the Coanda effect, a homogenization of the powder-air mixture is achieved during the formation of the mixing flow 7.3.At the same time, the Coanda effect prevents any influence on the bow's movement, resulting in an extremely smooth bow motion.

[0023] Regarding its mode of operation: The sheet smoother 4, which is present for front printing and generally deactivated for back printing, is used according to the invention to introduce powder into the sheet 5 from below without introducing further inhomogeneity into the sheet guide. The sheet smoother 4 thus acts accordingly as a powder applicator in a common assembly or in the immediate vicinity through the same gap in the sheet guide.

[0024] In the perfecting mode, a strong vacuum is created at the sheet flosser 4 by suction nozzles 4.6, which smooths the sheets 5 at the sheet flosser 4. The powder nozzles 4.4 are deactivated in this mode. Theoretically, however, powdering is also possible in perfecting mode.

[0025] Particularly in perfecting and double-sided printing, the underside of the sheet 5 is sprayed with a powder-air mixture from the sheet flosser 4. The mixture emerges from the powder nozzles 4.4, whose spray directions can assume any angle to the sheet 5 or the impact surface. The support nozzles 4.5 generate an overpressure within the sheet flosser 4 that guides the sheet 5, preventing contact between the underside of the sheet and the flosser 4. List of reference symbols used 1 display 2 arc guide cylinders 3 chain conveyor system 4 sheet smoothers 4.1 falling flank 4.2 Split floor 4.3 rising flank 4.4 Powder nozzles 4.5 Support nozzles 4.6 Suction nozzles 5 sheets 6 display stacks 7.1 Air cushion flow 7.2 Fanned powder flow 7.3 Mixing flow BFR Bow conveyor direction

Claims

[1] Surface treatment device in a sheet processing machine with a gap extending transversely to a sheet conveying direction (BFR), which is arranged at a distance from the sheet transport path and with means for applying a vacuum, which presses the sheet (5) conveyed past the gap against the gap for smoothing, where powder nozzles (4.4) for powdering the arc (5) are assigned to the gap, wherein the gap is assigned suction nozzles (4.6) as a bow smoother (4) for generating a vacuum and / or for extracting the powder, wherein the powder nozzles (4.4) are designed as impact nozzles which spray the powder against at least one impact surface and wherein the sheet smoother (4) is arranged in recesses of sheet guide plates below the sheet transport path in the delivery (1) of a sheet-fed printing press. [2] Device according to claim 1, characterized by, that the gap has a cross-section which, viewed in the arc conveying direction (AFR), comprises a falling flank (4.1), a gap bottom (4.2) and a rising flank (4.3). [3] Device according to claim 2, characterized by , that the flanks (4.1, 4.3) of the gap have a radius of curvature. [4] Device according to claim 2 or 3, characterized by , that the powder nozzles (4.4) are assigned to the falling flank (4.1) and / or the rising flank (4.3). [5] Device according to claim 2, 3 or 4, characterized by , that the powder nozzles (4.4) are assigned to the gap base (4.2). [6] Device according to any one of claims 1 to 5, characterized by , that the distance of the powder nozzles (4.4) to the sheet transport plane is variable. [7] Device according to any one of the preceding claims, characterized by , that support nozzles (4.5) are assigned to the falling flank (4.1), the gap base (4.2) and / or the rising flank (4.3). [8] Device according to claim 1, characterized by , that the negative pressure generated by the suction nozzles (4.6) is adjustable and / or controllable. [9] Device according to claim 1, characterized by , that the sheet-processing machine is designed as a printing machine and is switchable between the operating modes of single-sided printing and double-sided printing, whereby in single-sided printing the suction nozzles (4.6) and in double-sided printing the powder nozzles (4.4) and the support nozzles (4.5) can be activated. [10] Device according to claim 1, characterized by , that the impact nozzles are assigned to the falling flank (4.1) and spray the powder in arc conveying direction (BFR) against the rising flank (4.3) which is designed as an impact surface. [11] Device according to any one of the preceding claims, characterized by , that the powder nozzles (4.4) can be activated across the machine width according to the sheet format. [12] Method for acting on a sheet (5) in a sheet-processing machine which can be operated either in frontal printing or in frontal printing with a sheet smoother (4) for smoothing the sheets (5), wherein the sheets (5) are smoothed in the area of ​​the sheet smoother (4) in frontal printing mode and are powdered in the area of ​​the sheet smoother (4) in frontal printing mode.

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