Abstract:
A washing device for a cylinder in a printing press includes a washing cloth for removing contaminants and ink, etc. from the surface of the cylinder and an ultrasonic source directing sound energy onto the surface of the cylinder to assist a washing operation. A focusing device disposed in front of the ultrasonic source concentrates the sound energy on a substantially linear focus region on the surface of the cylinder, extending parallel to the axis of the cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2007 030 572.0, filed Jul. 2, 2007; the prior application is herewith incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a washing device for a cylinder in a printing press, having a washing cloth and an ultrasonic source which directs sound energy onto the cylinder surface. 
     A washing device of that type is known, for example, from International Publication No. WO 03/011599. There, in order to assist the washing operation, an ultrasonic source is provided which is intended to be used for the easier removal of contaminants and ink, etc. from the surface of the blanket stretched on a transfer cylinder in an offset printing press. Furthermore, German Published, Non-Prosecuted Patent Application DE 100 63 987 A1, corresponding to U.S. Pat. No. 6,865,986, describes a cloth washing device for a digital printing press. There, in order to clean the cylinder carrying the printing image, a cleaning band impregnated with a liquid can be acted upon on the cylinder surface by an ultrasonic actuator. Furthermore, German Published, Non-Prosecuted Patent Application DE 197 32 060 A1 describes a washing device for the blanket cylinder of an offset printing press which has an ultrasonic generator but no washing cloth. In that case, the intention is for the loosened dirt particles to be doctored off the cylinder surface by rubber lips. 
     In Patent Abstracts of Japan Publication No. JP 01170641, a use is described of a washing doctor vibrating in the ultrasonic range, which is in direct mechanical contact with the rubber surface. In apparatuses of that type, there is the risk that the cleaning liquid sprayed onto the blanket in front of the doctor will get into the printing press and cause damage there as a result of corrosion, etc. 
     The so-called cloth washing devices normally used heretofore in offset printing presses with which, during a job change, the inked blanket on the transfer cylinder is cleaned, normally have no ultrasonic sources to assist washing. Even without such assistance, the washing time is about 2 minutes, with the blanket being washed clean within 3 to 4 cylinder revolutions. Nevertheless, there is the desire to shorten the washing times with the effect of a rapid job change. However, that was not possible with the ultrasonic-assisted washing devices described in the prior art, the implementation of which failed due to the fact that the devices proposed required too much power. That is because, in order to achieve the ultrasonic cleaning action when sweeping over the blanket surface once, very high ultrasonic power densities are required on the inked blanket surface, as are otherwise known only from material processing and can be achieved, for example, with welding sonotrodes. Conventional inexpensive sound generators are not capable of making that requisite ultrasonic power available. Due to the low efficiency of the conversion from electric power into sound power, they themselves heat up very highly, which can lead to the destruction of the sound sources. Therefore, the previous proposals for improving the washing performance of blanket washing devices with the assistance of ultrasound have not been able to make progress. 
     It is known from ultrasonic diagnostics to focus the ultrasonic waves to produce ultrasonic images. However, configurations of that type are unsuitable for washing devices. 
     U.S. Pat. No. 5,803,099 discloses a washing tank having ultrasonic generators, with sound fields which are focused onto point-like regions by spherical ultrasonic lenses. That washing device is not suitable for the rapid cleaning of cylinder surfaces. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a washing device for a cylinder in a printing press, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, which shortens a washing operation considerably and which manages with an acceptable connected electric power. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a washing device for a cylinder in a printing press. The washing device comprises a washing cloth for removing at least contaminants and ink from a surface of the cylinder, an ultrasonic source directing sound energy onto the surface of the cylinder for assisting a washing operation, and a focusing device disposed in front of the ultrasonic source for concentrating the sound energy onto a substantially linear focus region on the surface of the cylinder extending parallel to an axis of the cylinder. 
     According to the invention, the sound energy emitted by one or more ultrasonic generators belonging to an ultrasonic source is concentrated onto a substantially linear focus region on the cylinder surface, extending parallel to the cylinder axis. To this end, use is advantageously made of a cylindrical ultrasonic lens, which includes a single or a plurality of cylindrical or toroidal sound lenses. In addition, the focusing device can also be formed through the use of a cylindrical concave shape of sonotrodes or ultrasonic oscillators. It is possible, of course, for the two measures, the cylindrical sound lens and the concave shape of the sonotrodes, to be combined with each other. The high sound energy density produced on the cylinder or blanket surface in the substantially linear focus region then loosens the ink or contaminants from the surface, with the dirt or ink particles being transported away by the wet washing cloth resting on the surface. In this case, it can be particularly advantageous if the washing cloth is moved away continuously over the linear focus region during the washing operation, while at the same time the cylinder rotates at a high surface speed counter to or in the direction of the washing cloth movement. 
     Furthermore, it is expedient to use the cylindrical sound lens, which produces the linear focus either on its own or together with other aids, to press the washing cloth against the cylinder surface to be cleaned. The construction becomes particularly simple when this cylindrical lens is formed as a tubular plastic part, in the interior of which the washing liquid for wetting the washing cloth or the cooling liquid for cooling the ultrasonic generator is contained. In this case, two or more functions, namely carrying the washing liquid or cooling liquid, focusing the ultrasonic energy and pressing the washing cloth onto the rubber or cylinder surface, are fulfilled by one component. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a washing device for a cylinder in a printing press, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a diagrammatic, cross-sectional view of a first exemplary embodiment of a modified pressing element of a blanket washing device according to the invention, for pressing a washing cloth against a blanket on a blanket cylinder; 
         FIG. 1A  is a fragmentary, perspective view of a sonotrode for facing the washing cloth; 
         FIG. 2  is a cross-sectional view of a second embodiment of a modified pressing element; 
         FIG. 2A  is a fragmentary, perspective view of a concave cylindrical lens; 
         FIG. 3  is a cross-sectional view of a third embodiment of a modified pressing element; 
         FIG. 3A  is a plan view of ultrasonic generators packed closely together and offset; 
         FIG. 4  is a cross-sectional view of a fourth embodiment of a modified pressing element; 
         FIG. 4A  is a fragmentary, plan view of a slide having recesses for receiving the ultrasonic generators; 
         FIG. 4B  is a perspective view of an ultrasonic generator; 
         FIG. 5  is a cross-sectional view of a fifth embodiment of a modified pressing element; 
         FIG. 6  is a cross-sectional view of a sixth embodiment of a modified pressing element; 
         FIG. 6A  is a fragmentary, perspective view of a tube for supporting an ultrasonic generator; 
         FIG. 7  is a cross-sectional view of a seventh embodiment of a modified pressing element; 
         FIG. 8  is an elevational view of a tube to be connected to a cooling unit; and 
         FIG. 9  is a cross-sectional view illustrating cylinders in a printing unit of an offset printing press. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 9  thereof, there is seen a diagrammatic illustration of cylinders in a printing unit of an offset printing press in a plane perpendicular to axes of the cylinders. Reference symbol PLZ designates a so-called plate cylinder, on which a printing plate inked by rolls of an inking unit FW is fixed through mountings in a clamping channel. During rotation of the cylinders, a printing image on the printing plate is transferred to a blanket GT, which is clamped on a blanket cylinder GTZ illustrated therebelow. Reference symbol PB designates a paper sheet, which is led through between the blanket cylinder GTZ and an impression cylinder GDZ and, in the process, is printed with ink by the blanket GT. 
     In order to wash the blanket, as is customary in offset printing presses, a blanket washing device GTW is provided, which, during a job change, can be set onto the blanket cylinder GTZ along the direction of an arrow P after the end of a printing operation. This washing device GTW normally contains a washing cloth  10  which, under cyclic clock control, is unwound from a first storage coil  11   a  and wound up on a second take-up coil  11   b  having a drive. In between, the washing cloth  10  is pressed by a pressing element  11  against the surface of the blanket GT to be cleaned. 
     Such blanket washing devices normally operate in such a way that the cylinder surface to be cleaned is rotated past under the washing cloth which is pressed thereon and the latter is cycled onward repeatedly step by step during one revolution in order to convey the inked strip-like region of the washing cloth repeatedly onward in the direction of the take-up coil  11   b . The washing device further contains a drive for the movement of the washing cloth and a device for the supply of washing liquid, if the storage or supply roll  11   a  is not already impregnated with washing liquid. 
       FIG. 1  shows, in more detail, in a section perpendicular to the cylinder axes, a first exemplary embodiment of a modified pressing element  11  according to the invention, which is part of the blanket washing device GTW. 
     In the exemplary embodiment according to  FIG. 1 , the pressing element  11  includes a U-shaped aluminum profiled part  12  which is provided with a longitudinal slot on a side with which it presses the washing cloth  10  against the blanket GT. Located in the interior of the profiled part  12  is an elongated sonotrode  13  having a structure illustrated in  FIG. 1A . The sonotrode  13  includes two strip-like masses  13   a  and  13   b , between which there is disposed a piezo-ceramic layer  13   c , which has metal electrodes vapor-deposited on both sides. The lower mass or part  13   b  of the sonotrode  13 , facing the washing cloth  10 , is shaped concavely on its underside  14  and focuses the ultrasonic power emitted onto a narrow, substantially linear focus region on the surface of the blanket GT. The sonotrode  13  is pressed by springs  16  against a seat provided with a seal  18  on inner sides of two limbs of the U-shaped profiled part  12 . Strips  12   a  in the profiled part  12  are used for positional fixing in the upper region of the part  13   a  of the sonotrode  13 . 
     As is illustrated in  FIG. 1 , the two rounded U-shaped limbs of the profiled part  12  press the washing cloth  10  against the surface of the blanket GT. In order to wet the washing cloth with washing liquid, small feed pipes  15  are provided along the profiled part  12  and open into channels  17 , through which the washing liquid travels into a space between the washing cloth  10  and the concave surface  14  of the sonotrodes  13  and fills that space. Through the use of the washing liquid, ultrasonic energy is led effectively to the surface of the blanket GT while avoiding excessive reflections and there it is able to loosen dirt and ink residues adhering to the blanket surface, due to establishing cavitation of gas bubbles that are produced in the liquid in a focus region. 
     Of course, it is also possible to place a plurality of individual shorter sonotrodes in the profiled part  12  instead of a single sonotrode  13 . The sonotrodes are then expediently driven with the same phase during the operation of the washing device, in order to avoid destructive interferences. In this case, it can also be expedient to provide webs between the two limbs of the U-shaped profiled part  12 , which permit sealing between the individual sonotrodes against the penetration of washing water into the interior of the housing or part  12 . In this case, the individual sonotrodes will expediently be inserted through closable openings on the top of the profiled part  12 . 
       FIG. 2  shows an alternative, second exemplary embodiment of the modified pressing element  11  according to the invention, which is part of the blanket washing device GTW. 
     In the exemplary embodiment according to  FIG. 2 , identical or similar parts are provided with a designation that is higher by 10, as compared with  FIG. 1 , for ease of understanding. 
     In contrast to the exemplary embodiment according to  FIG. 1 , a plurality of individual sonotrodes  23  are disposed one after another in the hollow U-shaped aluminum profiled part  22  which serves as a pressing element. For example, twenty pieces may be provided having a length of about 5 cm for the blanket cylinder of a printing press in the 105 cm format. These sonotrodes are pressed by springs  26  against the rear side of a concave cylindrical lens  29  made of plastic, which is pushed into the aluminum profiled part  22  over the length of the latter along grooves  22   b . The concave cylindrical lens  29  is also shown in  FIG. 2A . The sonotrodes  23  are secured against lateral displacement by strips  22   a  in the interior of the profiled part  22 . 
     A diaphragm  20  made of plastic, rubber or a porous ceramic, which limits the flow of liquid, is located over an opening  21  matched to an ultrasonic beam lobe between the two U-shaped limbs of the profiled part  22 . When choosing the material, the density of the diaphragm is expediently matched to the density of the washing liquid, in order to avoid undesired reflections of the ultrasonic energy at the interface with the diaphragm  20 . The diaphragm  20  limits the flow of the washing liquid from the small feed pipes  25  into the washing cloth  10  and ensures that no washing liquid emerges when the washing process has been completed and the pressure in the small feed pipes  25  is switched off. 
     The cylindrical plastic lens  29  is formed of PLEXIGLASS®, which is polymethyl methacrylate. Since the speed of sound in this material is virtually twice as high as in water, the planoconcave cylindrical lens acts as a converging lens and concentrates the ultrasonic power in a very narrow linear region, as is indicated by arrows. 
     Of course, given appropriate dimensioning of the radius of the cylindrical lens and its distance from the surface of the blanket, it is also possible to use other plastics such as polyacrylate, etc. 
     The use of a plurality of individual sonotrodes results in the advantage that the length of the pressing element of the blanket washing device can be matched to different format widths without specific individual sonotrodes having to be fabricated for the format in each case. In the same way, instead of the cylindrical lens made of plastic, a number of individual toroidal or cylindrical individual lenses can be provided, each being assigned to the individual sonotrodes. In this case, a toroidal form of the individual lenses assists the uniformity of the propagation of sound along the cylinder surface beyond regions switched off by webs. 
       FIG. 3  shows a third exemplary embodiment of the modified pressing element  11  according to the invention, which is part of the blanket washing device GTW. 
     In the exemplary embodiment according to  FIG. 3 , the cubical sonotrodes are replaced by ultrasonic generators  33   a ,  33   b  . . . with a circular cross section. Such ultrasonic generators can be procured inexpensively as bought in parts, since they are used in high numbers in other applications. In the present case, the ultrasonic generators  33   a ,  33   b  . . . are not disposed one after another in a line but packed closely against one another with an offset and in each case inclined alternately with respect to one another, as is illustrated in  FIG. 3A . Springs  36   a ,  36   b  . . . respectively assigned to the ultrasonic generators press the ultrasonic generators  33   a ,  33   b  . . . onto a prismatic strip  38 , which is adhesively bonded to the rear of a cylindrical lens  39 . The prismatic strip  38  is composed of the same material as the cylindrical lens  39 , so that impedance steps, such as otherwise occur at the transition into another medium, are avoided. 
       FIG. 4  shows a fourth exemplary embodiment of the modified pressing element  11  according to the invention, which is part of the blanket washing device GTW. 
     In the exemplary embodiment according to  FIG. 4 , simple, inexpensive, cylindrical ultrasonic generators  43  are likewise used, but they are inserted one after another with their axes parallel to one another into circular recesses in lower and upper slides  41   a ,  41   b , as shown in  FIG. 4A . The array of cylindrical ultrasonic generators formed in this way is inserted at the end into an aluminum profiled part  42  illustrated in  FIG. 4 . The lower slide  41   a , facing the blanket GT, rests on a shoulder  42   a  in the interior of the profiled part  42  over a sealing strip  48 . The interior of the profiled part  42  above the part  41   a  is filled with oil, which is used to dissipate the heat produced in the ultrasonic generators  43 . A lower side  44  of the ultrasonic generators  43 , facing the washing cloth  10 , is shaped cylindrically concavely, as shown in  FIG. 4B . Axes K of the cylindrically concave recesses of all of the ultrasonic generators  43  accommodated behind one another in the slides  41   a ,  41   b  are aligned in a line parallel to the axis of the blanket cylinder GTZ. In this way, the ultrasonic energy emitted by the ultrasonic generators  43 , as illustrated by arrows in  FIG. 4 , is focused substantially onto a narrow linear region parallel to the cylinder axis on the surface of the blanket GT, given a suitable choice of the radius of curvature of the concavely cylindrical recess  44  in the ultrasonic generators  43  and the spacing of the ultrasonic generators from the washing cloth. 
       FIG. 5  shows a fifth exemplary embodiment of the modified pressing element  11  according to the invention, which is part of the blanket washing device GTW. 
     In the exemplary embodiment according to  FIG. 5 , as opposed to that according to  FIG. 4 , the aluminum profiled part  42  has been replaced by a plastic profiled part  52 . The profiled part  52  has a U-shaped cross section and, on its side facing the washing cloth  10 , is closed like a trough, while its two limbs having a U-shaped cross section on the opposite side are closed at the top by a cover  57 . On the outside, for the purpose of reinforcement and to dissipate heat, the plastic profiled part  52  bears a plurality of ribs  51  extending over its entire length. The outer circular cross section of the profiled part  52  on the side toward the washing cloth is flattened and matched to the radius of the blanket GT. In this way, in the region in which it rests on the washing cloth  10 , the wall of the profiled part  52  is already given the shape of a concave cylindrical lens, which once more focuses the ultrasonic energy emitted from the underside of the ultrasonic generators  53  inserted into the profiled part before the energy strikes the blanket, and focuses it in a linear region of a blanket surface. 
     The ultrasonic generators  53  are the same as those according to  FIG. 4  but are placed from above in the plastic profiled part  52  with the cover  57  removed, on strips  52   a  in the profiled part  52 . Pins  58  in conjunction with a longitudinal groove  59  in the ultrasonic generators act as an anti-rotation safeguard and hold the generators  53  in their place. The interior of the profiled part  52  is filled with a nonconductive liquid which has a considerably lower density than the material of the plastic profiled part  52 . In this way, a biconvex liquid rod  60  between the concave undersides of the ultrasonic generators and the concave inner side of the profiled part  52  acts as a cylindrical converging lens, by which the ultrasonic power is focused on a linear region. The nonconductive liquid additionally serves to absorb the heat loss produced during the operation of the ultrasonic generators  53 , in order to ensure that the generators  53  do not heat up excessively. 
     In this exemplary embodiment, the washing liquid is sprayed onto the washing cloth  10  by separate spray nozzles  55  beside the pressing element. The washing cloth  10  is moved at a slow speed past the pressing element during the washing, while at the same time the cylinder GTZ having the blanket GT moves the blanket GT under the pressing element and the washing cloth  10  in the opposite direction. 
       FIG. 6  shows a sixth exemplary embodiment of the modified pressing element  11  in accordance with the invention, which is part of the blanket washing device GTW. 
     In the exemplary embodiment according to  FIG. 6 , the housing of the pressing element includes a stable metal housing with an H-shaped cross section which is open at the top and bottom. Holes are provided close together in a cross strut  62   c  of a profiled part  62  connecting two limbs  62   a  and  62   b , to accommodate cylindrical ultrasonic generators  63 , which are plugged into the holes. 
     A lower region of the limbs  62   a  and  62   b  tapers somewhat toward the center. A plastic tube  69 , which is inserted into this region, is made of a material having a very much higher density than the washing liquid, such as polyethylene. This plastic tube is flattened at the top and bottom on both sides. Flat undersides of the ultrasonic generators  63  are placed on the upper flattened portion, while the plastic tube  69  is placed with its lower flattened portion on the washing cloth  10  and is pressed onto the latter by springs  66  acting through the ultrasonic generators  63  when the washing device with the profiled part  62  is fed in the direction of the blanket GT. 
     Capillaries  67 , through which the washing liquid emerges under appropriate pressure and wets the washing cloth  10 , are introduced into the tube in the region of the lower flattened portion. 
     In this exemplary embodiment, the cylindrical liquid rod of the washing liquid, in conjunction with the planoconcave cylindrical lenses of the flattened portions of the plastic tube  69 , focuses the ultrasonic energy in the desired way onto a narrow linear region. In addition, in this exemplary embodiment, the springs  66  perform a dual function: they press the ultrasonic generators  63  firmly onto their seat and they press the tube part  69  of the pressing element firmly against the washing cloth  10 . 
       FIG. 7  shows a seventh exemplary embodiment of the modified pressing element  11  in accordance with the invention, which is part of the blanket washing device GTW. 
     In the exemplary embodiment according to  FIG. 7 , the pressing element for the washing cloth  10  is composed overall of a thick-walled plastic tube  79 , that is closed on both sides and, as is seen from the view according to  FIG. 7 , is provided on respective sides with an inlet connecting piece  78   a  and an outlet connecting piece  78   b  for the washing liquid. The tube  79  is connected to a cooling unit, through which the heat loss arising during the washing operation is dissipated through the ultrasonic generators. The plastic tube  79  is composed of the same material as the tube  69  of  FIG. 6  and likewise bears a flattened portion on its underside, which is provided with capillaries  77  for the passage of the washing liquid. 
     A metal profiled part  72  is pushed into the plastic tube  79  and is held there by two projections  71   a  and  71   b  in corresponding grooves in the plastic tube  79 . A plurality of ultrasonic generators  73  having a rectangular cross section in encapsulated form are accommodated close together in the metal profile  72 , with their undersides being cylindrically concavely shaped as in the exemplary embodiment according to  FIG. 1 . Due to this concave shape, a wedge of the washing liquid  70  between the undersides of the ultrasonic generators  73  and the concave inner side of the tube  79  becomes a “thick cylindrical lens” and focuses the ultrasonic waves on a linear region. In this exemplary embodiment, the washing liquid  70  also serves simultaneously to cool the ultrasonic generators.