WO2011064129A1

WO2011064129A1 - Printing cylinder arrangement for a rotary printing machine

Info

Publication number: WO2011064129A1
Application number: PCT/EP2010/067696
Authority: WO
Inventors: Andreas Kückelmann; Wolfgang Brusdeilins; Bodo Steinmeier; Thomas Boje
Original assignee: Fischer & Krecke Gmbh
Priority date: 2009-11-25
Filing date: 2010-11-17
Publication date: 2011-06-03
Also published as: DE102009055767A1; WO2011064129A8

Abstract

Printing cylinder arrangement for a rotary printing machine, comprising a mandrel (12) that is rotatably supported in a machine frame (14) and a sleeve (16) that surrounds the mandrel with a spacing and has both its ends rigidly supported on the mandrel via disks (18), characterised in that a vibration dampening device (36A) for dampening bending oscillations of the mandrel (12) is arranged inside the sleeve (16).

Description

PRINTING CYLINDER ARRANGEMENT FOR A ROTARY

PRINTING MACHINE

The invention relates to a printing cylinder arrangement for a rotary printing machine, comprising a mandrel that is rotatably supported in a machine frame, and a sleeve that surrounds the mandrel with a spacing and has both its ends rigidly supported on the mandrel via disks.

US 3 378 902 A discloses a printing cylinder arrangement of this type, wherein the disks are hydaulically clamped on the mandrel by means of hydro-bushings. The rigid support and clamping of the disks on the mandrel has the advantage that the sleeve, which has a large bending strength thanks to its large radius, will also stabilize the mandrel, so that the printing cylinder arrangement as a whole will have a high bending strength. The rigid support has the further advantage that the printing cylinder arrangement will not yield to radial forces that act upon the sleeve during the printing operation when the sleeve rolls over the peripheral surface of an impression cylinder. This permits to achieve a high print quality.

EP 1 025 996 Al describes a similar printing cylinder arrangement in which the sleeve is essentially formed by a wound structure of carbon fibers. This arrangement has a very high rigidity combined with a small total weight, which results in smooth rolling properties and a correspondingly high print quality.

US 5 819 657 A discloses a printing cylinder arrangement in which the sleeve is supported on the mandrel via three or more disks that are distributed over the length of the printing cylinder. However, the disks are not directly supported on the mandrel, but on a hollow cylinder that includes at least one compressible layer and engages the periphery of the mandrel with its inner peripheral surface. In order to reduce friction, when the sleeve is thrust onto the mandrel or withdrawn therefrom, compressed air is used for forming an air cushion between the peripheral surface of the mandrel and the inner surface of the hollow cylinder. Yet, this solution has the drawback that the compressible layer of the hollow cylinder implies a higher resilience of the sleeve against the radial forces.

Especially in relief printing and flexographic printing, it is a general problem that the printing cylinder is subject to at least one radial blow in each revolution, when the edge of the printing plate or the printing pattern reaches the nip between the printing cylinder and the impression cylinder and the elevated, printing parts of the printing pattern hit the print substrate that is supported on the surface of the impression cylinder. These shocks or blows can excite vibrations in a very large frequency range. When, due to this effect, high-frequency natural oscillations of the printing cylinder are excited, this may lead to undesirable artefacts in the printed image.

DE 197 19 635 Dl describes a printing cylinder arrangement in which this problem shall be mitigated by the use of vibration-dampening bearings for the printing cylinder. This, however, leads again to the drawback that the vibration-dampening bearings make the printing cylinder arrangement as a whole more resilient against radial forces.

Although the construction that has been described in the opening paragraph achieves already a high overall rigidity, thanks to the rigid support of the sleeve, the mandrel which is made of steel must have a certain minimum cross-section in order to assure that the mandrel itself has a high bending strength and the natural vibrations thereof are in a frequency range as high as possible, in which no excitations will normally occur during the printing operation.

The larger the diameter of the mandrel, the higher is the total weight and the higher are the material costs. Further, the utility of the printing cylinder arrangement for short repeats is limited because a decreased repeat means that also the outer perimeter of the printing cylinder sleeve must decrease, and, on the other hand, this outer perimeter must be larger than the perimeter of the mandrel.

It is an object of the invention to provide a printing cylinder arrangement which can achieve smooth running properties and a high print quality with a comparatively small cross-section of the mandrel.

According to the invention, this object is achieved by the feature that a vibration dampening device for dampening bending oscillations of the mandrel is arranged inside the sleeve.

Since the bearing points at which the mandrel is supported in the machine frame are arranged outside of the disks that support the sleeve, a radial force that acts upon the sleeve creates a bending moment that can excite bending oscillations of the mandrel. In this case, the bending deformation of the mandrel will occur mainly inside of the sleeve, more specifically in the range between the two disks. The vibration dampening device according to the invention intervenes at this location for effectively attenuating the bending oscillations of the mandrel. The rigid support of the sleeve on the mandrel and the radial stiffness of the bearing of the mandrel in the machine frame are retained.

Since the bending oscillations of the mandrel are suppressed, it is possible to operate the printing machine at a higher printing speed and with a correspondingly increased number of revolutions of the printing cylinder without exciting any substantial resonance oscillations of the mandrel. Conversely, for a given number of revolution and given demands on the quality of the printed image, the cross-section of the mandrel can be reduced, so that weight and costs are saved and smaller repeats become possible.

Useful details and further developments of the invention are indicated in the dependent claims. The vibration dampening device may be an active or a passive dampening device. In an active dampening device, actuators are operated by an electronic control system in such a manner that the excitations that act upon the printing cylinder arrangement from outside are essentially compensated. Up to now, it has however been difficult to find actuators and electronic control systems that are fast and precise enough for effectively attenuating high frequency vibrations. For this reason, at present, a passive vibration dampening device is preferred, the function principle of which is mainly based on the consumption of vibration energy.

Embodiment examples will now be explained in detail in conjunction with the drawings, wherein:

Fig. 1 shows a schematic longitudinal section of a printing cylinder arrangement according to the invention;

Fig. 2 shows a cross-section of a dampening device in a printing cylinder arrangement according to another embodiment; and

Fig. 3 to 6 are schematic longitudinal sections of printing cylinder arrangements according to further embodiment examples.

Fig. 1 shows a printing cylinder arrangement 10 having a steel mandrel 12 that is rotat- ably supported in a frame 14 of a rotary printing machine, e.g. a flexographic printing machine. The mandrel is surrounded, with a certain spacing, by a cylindrical sleeve 16 that may for example be made of carbon fiber-reinforced resin and may support printing plates or a printing sleeve (not shown) on its outer periphery. At both ends, the sleeve 16 is rigidly supported on the mandrel 12 by disks 18 which may be somewhat inwardly offset relative to the ends of the sleeve.

In the example shown, each of the disks 18 has, at its inner peripheral edge, a rigid boss 20 that tightly embraces a hydro-bushing 22 that is embedded in the mandrel 12 and is flush with the peripheral surface thereof. Thus, the disks 18 and the sleeve 16 form a rigid unit that may rigidly be clamped to the mandrel 12 by means of the hydro-bushing 22.

One end of the mandrel 12, the left end in Fig. 1, is supported in a removable bearing 24, whereas the opposite end is supported in two bearings 26 that are spaced apart from one another in axial direction. Thus, when the bearing 24 is removed, the mandrel 12 with the sleeve 16 arranged thereon is held by the two bearings 26, 28 in cantilever fashion.

On the side of the removable bearing 24, the machine frame has a window 34 through which the sleeve 16 may be removed. The hydro-bushings 22 are connected to a hydraulic pressure source (not shown) via a piping system 30 passing through the mandrel 12. When this hydraulic system is not under pressure, the hydro-bushings 22 release the bosses 20, so that the sleeve 16, including the disks 18, may axially be withdrawn from the mandrel 12. When the printing machine is to be prepared for another print job, another sleeve may be thrust onto the mandrel 12 and may be fixed by means of the hydro-bushings 22.

The bearings 24, 26 and 28 are mounted in bearing blocks (not shown) and are movable within the machine frame 14. During the printing operation, the printing cylinder arrangement 10 is set against the peripheral surface of an impression cylinder (not shown) over which a printing substrate is passed. The peripheral surface of the sleeve 16 is pressed against the print substrate with a certain force, so that corresponding reaction forces act upon the sleeve 16 in radial direction, e.g. in direction of the arrows A in Fig. 1. These radial forces are transmitted onto the mandrel 12 via the disks 18 that are taken up by the bearings 24 and 26 in outwardly offset positions. This results in force couples that have the tendency to bend the mandrel 12, as has exaggeratedly been shown in dash-dotted lines in Fig. 1. During the print operation, this mechanism can cause the mandrel 12 to be excited to bending oscillations which act back onto the sleeve 16 via the disks 18 and may result in undesired artefacts in the printed image.

In order to suppress these bending oscillations, a passive vibration dampening device 36A is arranged inside the sleeve 16.

In the example shown in Fig. 1, the vibration dampening device 36A is formed by an additional disk 38 that is disposed centrally between the disks 18 and embraces the periphery of the mandrel 12 with its boss 40. In this position, another hydro-bushing 42 that is connected to the same piping system 30 as the hydro-bushings 22 is embedded in the peripheral surface of the mandrel 12. Thus, when the hydraulic system is pressurised, the disk 38 is also clamped on the mandrel 12. However, unlike the bosses 20 of the outer disks 18, the boss 40 is not entirely rigid but includes an annular layer 48 of compressible, vibration-dampening material.

As is shown in Fig. 1, the vibration dampening device 36A is located at the position of the mandrel 12 where the bending oscillation (basic oscillation) of the mandrel has the largest amplitude. The part of the boss 40 that is secured on the hydro-bushing 42 follows the oscillations of the mandrel 12, whereas the radially outward part of the disk 38 is firmly connected to the sleeve 16 which has a high bending strength, thanks to its large radius and the material of which it is made. Consequently, the compressible material in the layer 48 is alternatingly compressed and expanded, whereby vibration energy is consumed.

The layer 48 of compressible material does not have to be positioned inside the boss 40 but may optionally be arranged in an outer part of the disk 38.

Whereas, in Fig. 1, only a single vibration dampening device 36A is disposed centrally between the disks 18, in a modified embodiment, a plurality of such vibration dampening devices could be distributed over the length of the mandrel 12, so that higher harmonic oscillations of the mandrel could also be dampened effectively. Fig. 2 shows a vibration dampening device 36B which has a similar construction as the device 36 A shown in Fig. 1, wherein, however, the hydro-bushing 42 is used as a vibration-attenuating member. In this case, the boss 40 which has been shown in cross- section in Fig. 2 does not have to have the layer 48 of compressible material. The hydro-bushing 42 is internally formed with an annular chamber 50 filled with a hydraulic fluid that is supplied via the piping system 30 as in Fig. 1, for example. The radial dimensions of the annular chamber 50 are exaggerated in Fig. 2. When the mandrel is excited to bending oscillations, the radial width of the annular chamber 50 is reduced at one point of its periphery and increased on the diametrically opposite side, so that the hydraulic fluid is displaced and flows through the annular chamber 50 in circumferential direction. Inside the annular chamber 50, radial ribs 52 or orifices or the like form a throttle member which restricts the flow of the hydraulic fluid and thereby effects a hydraulic attenuation of the oscillation.

In a modified embodiment, the hydraulic fluid, at least the one in the hydro-bushing 42, may be a non-Newtonian liquid the viscosity of which increases sharply in case of shock-like shear stresses and pressure changes, so that high-frequency vibrations can be dampened very efficiently, whereas the liquid behaves like a low-viscosity liquid under stationary pressure conditions. Optionally, the hydraulic fluid may also be an electro- rheologic liquid the viscosity of which can be influenced by applying an electric voltage. This permits to optimise the vibration dampening characteristics by varying the applied voltage while the printing machine is running.

Figs. 3 shows an embodiment having a hydraulically adjustable vibration dampening device 36C that is completely integrated in the boss 40 of the disk 38.

The boss 40 is formed with a conical cavity that accommodates a slotted conical ring 54. The inner peripheral surface of the conical ring 54 engages the peripheral surface of the mandrel 12 via a layer 56 of compressible, vibration-dampening material. On the side of the conical ring 54 that has the larger cross-section, several pistons are evenly distributed over the circumference of the ring, and each piston is guided in a hydraulic chamber 60. The hydraulic chambers, only one of which is visible in Fig. 3, communicate with one another, and one of them is delimited on the outer side of the boss 40 by a screw 62 that has a female plug-connector for an adjusting rod 64. A bore 66 in the disk 18 on the side of the bearing 24 permits to insert the adjusting rod 64 from the operating side of the printing machine into the sleeve 16 and to couple it co-rotatably to the screw 62, so that the latter may be screwed deeper into the hydraulic chamber 60 in order to increase the hydraulic pressure. As a result, the slotted conical ring 54 is displaced in the conical cavity of the boss 40 so that it fits closer around the periphery of the mandrel 12.

Once the sleeve 16 has been thrust onto the mandrel 12 and has been clamped by means of the hydro-bushings 22, the adjusting rod 64 is used for pressurizing the hydraulic chambers 60, so that the disk 38 will also be clamped firmly on the mandrel. By suitably selecting the pressure, the dampening effect of the compressible layer 56 can be adjusted.

Fig. 4 shows an embodiment having a vibration dampening device 36D which is different from the device 36C shown in Fig. 3 in that the adjustable dampening effect is not achieved by means of a conical ring having a compressive layer but by means of a multi-disk coupling 68. Here, the hub 40 is firmly clamped on the mandrel 12 by means of a hydro-bushing 22 connected to the piping system 30, whereas the disk 38 surrounds the boss 40 with radial play and is connected to the boss only via the multi-disk coupling 68. In this case, the hydraulic pressure in the hydraulic chambers 60 serves for actuating the multi-disk coupling 68 via a pressure ring 70.

In this embodiment, the vibration energy of the mandrel 12 is consumed by friction or shear stresses in the disks of the multi-disk coupling 68. The amount of the dampening effect can be adjusted by means of the adjusting rod 64 independently of the hydraulic pressure in the piping system 30. Thus, the sleeve 16 may be removed from the mandrel and may be re-installed without necessity to re-adjust the vibration dampening system.

Fig. 5 shows an embodiment having a vibration dampening device 36E that fills the entire space between the disks 18. The bosses of the disks 18 are connected by a thin- walled tube 72 that fits around the peripheral surface of the mandrel 12 and can slightly be expanded elastically. This tube 72 is surrounded by a layer 74 of compressible, vibration-attenuating material, and the latter is again surrounded by a less compressible layer 76 of filling material that fills the entire space up to the internal surface of the sleeve 16.

In addition to the piping system 30 for the hydro-bushings 22, the mandrel 12 has a pneumatic piping system 78 via which compressed air can be supplied to nozzles 80 that are distributed on the peripheral surface of the mandrel 12.

When the sleeve 16 is to be thrust onto the mandrel 12, the nozzles 80 serve to create an air cushion that reduces the friction between the tube 72 and the mandrel 12. When, subsequently, the sleeve is clamped on the mandrel by means of the hydro-bushings 22, the supply of compressed air is switched off, so that the tube 72 closes tightly around the peripheral surface of the mandrel. Then, the vibrations of the mandrel 12 are attenuated on the entire length of this mandrel, mainly by the compressible layer 74.

Fig. 6 shows a vibration dampening device 36F which differs from the device 36E shown in Fig. 5 in that the tube 72 of elastic and compressible material is surrounded by an alternating sequence of rings 82 made of a relatively stiff material and thinner rings 84 made of compressible, vibration-dampening material. The rings 82, 84 completely fill the space between the bosses of the disks 18, but their radius is smaller than the inner radius of the sleeve 16. In this case, bending oscillations of the mandrel 12 have the effect that the rings 84 are alternatingly compressed and expanded at certain points of their periphery. As a result, vibration energy is consumed mainly by the compressible rings 84.

Claims

1. Printing cylinder arrangement for a rotary printing machine, comprising a mandrel (12) that is rotatably supported in a machine frame (14), and a sleeve (16) that surrounds the mandrel with a spacing and has both its ends rigidly supported on the mandrel via disks (18), characterised in that a vibration dampening device (36A - 36F) for dampening bending oscillations of the mandrel (12) is arranged inside the sleeve (16).

2. Printing cylinder arrangement according to claim 1, wherein the vibration dampening device (36A - 36F) is a passive vibration dampening device.

3. Printing cylinder arrangement according to claim 1 or 2, wherein the sleeve (16) is arranged to be withdrawn from the mandrel (12) in axial direction.

4. Printing cylinder arrangement according to claim 3, wherein at least one additional disk (38) is provided between the two disks (18) that are rigidly supported on the mandrel (12), said additional disk coupling the sleeve (16) with the mandrel (12) via the vibration dampening device (36 A - 36D).

5. Printing cylinder arrangement according to claim 4, wherein the rigidly supported disks (18) and the additional disk (38) are adapted to be hydraulically clamped on the mandrel (12).

6. Printing cylinder arrangement according to claim 5, wherein hydro-bushings (22, 42) for hydraulically clamping the rigidly supported disks (18) and a radially inner part (40) of the additional disk (38) are connected to a common hydraulic piping system (30).

7. Printing cylinder arrangement according to claim 4 or 6, wherein the vibration dampening device (36A; 36C) comprises at least one layer (48; 56) of compressible material that is arranged between a radially inner part and a radially outer part of the additional disk (38).

8. Printing cylinder arrangement according to any of the preceding claims, wherein the dampening effect of the vibration dampening device (36b - 36D) is hydraulically adjustable.

9. Printing cylinder arrangement according to the claims 4 and 8, wherein the vibration dampening device (36B) comprises a vibration-dampening hydro-bushing (42) with which the additional disk (38) is clamped on the mandrel (12).

10. Printing cylinder arrangement according to claim 8, wherein the vibration dampening device (36C) comprises a conical ring (54) adapted to be fitted around the peripheral surface of the mandrel (12) by hydraulic pressure.

11. Printing cylinder arrangement according to claim 8, wherein the vibration dampening device (36D) comprises a multi-disk coupling (68) between a radially inner part (40) and a radially outer part of the disk (38).

12. Printing cylinder arrangement according to claim 3, wherein the vibration dampening device (36E; 36F) comprises a tube (72) tightly fitted around the mandrel (12), and the mandrel (12) includes a pneumatic piping system (78) and nozzles (80) for creating an air cushion between the peripheral surface of the mandrel (12) and the inner surface of the tube (72).

13. Printing cylinder arrangement according to claim 12, wherein the vibration dampening device (36E; 36F) extends over the entire length of the part of the mandrel (12) situated between the disks (18).

14. Printing cylinder arrangement according to claim 13, wherein the vibration dampening device (36E) fills the entire internal space of the sleeve (16) between the disks (18).

15. Printing cylinder arrangement according to claim 13 or 14, wherein the vibration dampening device (36F) includes at least one vibration-dampening ring (84) that is fitted around the tube (72) and supported between the disks (18) in such a manner that, when the mandrel (12) is bent, the ring is axially compressed at one point of its periphery and expanded at an opposite point of its periphery.