Patent Publication Number: US-2004050277-A1

Title: Cleaning method and device for a printing roller

Description:
[0001] The invention relates to a printing-press roll cleaning method and a printing-press roll cleaning apparatus as claimed in the patent claims.  
       [0002] Accordingly, the invention relates to a printing-press roll cleaning method for cleaning rotating rolls in a roll train which contains a plurality of successive rolls resting on one another, comprising at least one driven roll and at least one non-driven roll, which can be driven only by peripheral surface contact with an adjacent roll, in particular inking unit rolls of an inking unit for offset printing, liquid being applied by machine to the peripheral surface of at least one of these rolls in order to loosen contamination, via discharge openings in a liquid application apparatus, which has a plurality of discharge openings distributed over the roll length, in addition the liquid being transferred from peripheral surface to peripheral surface of the rolls by the rotation of the rolls in the nip, and the liquid, together with the dirt loosened by it, in particular ink and paper dust, being wiped off on another of the rolls by a wiping apparatus.  
       [0003] Furthermore, the invention relates to a printing-press roll cleaning apparatus for cleaning rotating rolls in a roll train which contains a plurality of successive rolls resting on one another, comprising at least one driven roll and at least one non-driven roll which can be driven only by peripheral surface contact with an adjacent roll, in particular inking unit rolls of an inking unit for offset printing, the cleaning apparatus containing a liquid application apparatus with a plurality of discharge openings distributed over a roll length, through which liquid can be applied by machine to the peripheral surface of et least one of the rolls to loosen dirt, in particular ink and paper dust, the liquid being transferred from peripheral surface to peripheral surface in the nip by the rotation of the rolls and it being possible for the liquid, together with the dirt loosened by it, to be wiped off on another of the rolls by a wiping apparatus.  
       [0004] Prior Art:  
       [0005] Inking rolls of an inking unit in a printing unit for offset printing are wetted with liquid by means of what is known as a spray pipe in order to loosen the ink, said liquid being sprayed onto one of the rolls and doctored off on another roll. One or more of the inking unit rolls is/are driven, while other rolls are not driven, but are only co-rotated by the contact between their roll periphery and the roll periphery of an adjacent roll. The cleaning operation must be carried out in a short time in order to shorten the down times for printing operation. The liquid must therefore be transferred as quickly as possible and uniformly to all the rolls in the roll train from the roll which is wetted with the liquid from the spray pipe. If little liquid is sprayed onto the one roll, it takes a long time until all the rolls are wetted. If a great deal of liquid is sprayed onto the one roll, there is the risk that the liquid will back up in the nip or even upstream of the latter in the roll pocket and, as a result, will flow out of the roll train laterally in the roll longitudinal direction. Furthermore, there is the risk of overwetting the first or a plurality of following rolls in the roll train, so that the non-driven rolls, because of a lack of adhesive friction, are no longer co-rotated by the adjacent roll or stop and rotate in leaps and bounds and, in the process, throw off liquid mixed with loosened ink. The liquid, and therefore also the ink loosened by it, will no longer be transferred to the stationary roll and thus not transferred to the doctor apparatus of the doctored roll either. The inking unit will therefore no longer be cleaned adequately, so that it has to be cleaned manually.  
       [0006] The invention is intended to achieve the object of achieving reliable cleaning of all the rolls in a roll train in a short time in a simple and inexpensive manner.  
       [0007] According to the invention, this object is achieved by the defining features of claim 1 and of claim 7, respectively.  
       [0008] Claim 1 is defined by the fact that the liquid jets are applied only to individual narrow wetting zones corresponding to their width on the at least one roll, leaving non-wetting zones between them, the liquid being applied to the at least one roll in such a low quantity per unit time that the liquid only flows away laterally over the entire width of the non-wetting zones during a large number of roll revolutions, and, in the case of at least some of the rolls in the roll train following the one roll, in the nip of the rolls resting on one another, the liquid is initially likewise transferred only to wetting zones of the respective next roll, leaving non-wetting zones between them, and the liquid then flowing away laterally over the entire width of the non-wetting zones only after a plurality of roll revolutions, so that between the non-driven roll and the roll or rolls resting on it, a sufficient frictional resistance in order to drive it along in rotation is always ensured.  
       [0009] Claim 7 is defined by the fact that the discharge openings have an opening form and a distance from one another in the roll longitudinal direction such that the liquid jets, over their entire length and when they strike the at least one roll, have a spacing from one another in the roll longitudinal direction and, as a result, form individual wetting zones on the roll, corresponding to their jet width, leaving non-wetting zones between them, which no liquid jets strike.  
       [0010] Further features of the invention are contained in the subclaims.  
       ADVANTAGES OF THE INVENTION  
       [0011] The invention ensures that the liquid is applied and distributed quickly in a short time to all the rolls up to and including the doctored roll. The invention prevents overwetting of rolls and, as a result, prevents non-driven rolls slipping or remaining stationary. Stationary rolls prevent the transfer of liquid to further rolls and, as a result, have the effect of backing up liquid in the roll pocket, from which liquid is then squeezed out laterally. The non-wetting zones ensure adequate adhesive friction between the rolls, by means of which all the non-driven rolls are co-rotated by adjacent rolls and no rolls slip because of overwetting of the adjacent roll. Furthermore, a rapid transfer of liquid to all the rolls is achieved. The invention uses substantially fewer discharge openings or nozzles than the prior art.  
       [0012] “Liquid” can be solvent, detergent, water containing detergent or solvent, water with one or more additives which influence the printing process, pure water or any other liquid. Furthermore, the type of liquid can be changed during the washing operation. For example, at the start, detergent or solvent or water containing one can be used to loosen ink from the rolls, and can be rinsed afterwards with clear water. “Rolls” also include press cylinders, but in particular inking unit rolls.  
       [0013] “Driven roll”: a roll can be driven by an electric motor, by a pneumatic motor or a hydraulic motor or by means of a drive connection from another roll or another cylinder in the press.  
       [0014] “Non-driven roll” is a roll which rotates only because it rests on an adjacent roll and is co-rotated by the latter by the frictional resistance.  
       [0015] “Point-like cross section of the liquid jets” means a jet with a small cross section and spacing from one another over the entire jet length from the nozzle as far as the point at which it strikes the roll, as opposed to a spray jet or a very wide flat jet, which touch one another or mix with one another as soon as they strike the roll or even previously.  
       [0016] “wiping apparatus” for wiping the liquid and the roll contamination possibly loosened by it: this can be a doctor, a brush or a cloth or another element with which the liquid and, if appropriate, dirt loosened by the latter, can be removed from a roll. 
     
    
    
     [0017] The invention will be described below with reference to the drawings and using preferred embodiments as examples. In the drawings:  
     [0018]FIG. 1 shows, schematically, a side view of a printing unit with an inking unit and a damping unit,  
     [0019]FIG. 2 shows, schematically, a plan view of a particular embodiment of the invention,  
     [0020]FIG. 3 shows a cross section along the plane III-III of a spray pipe from FIG. 2. 
    
    
     [0021]FIG. 1 shows, schematically and not to scale, a printing unit containing a plate cylinder  2 , a blanket cylinder  3  contacting the latter, an impression cylinder  4  contacting said blanket cylinder  3 , an inking unit  6  and a damping unit  8 . This is therefore a damping-solution liquid offset printing unit. However, the invention can also be used for a dry offset printing unit. The printing unit can be part of a sheet-fed offset press (printing sheets) or a web-fed offset press (printing web-like printing material). The invention can also be used for other types of presses (relief printing, gravure printing).  
     [0022] The printing material  10  (sheet or web) runs through the nip  11  between the blanket cylinder  3  and the impression roll  4 . The printing image is transferred from the plate cylinder  2  to the blanket cylinder and from the latter to the printing material  10 .  
     [0023] The inking unit  6  can be of any desired type which contains at least one inking roll driven by a motor and at least one non-driven inking roll, the latter being driven by means of the frictional resistance of its peripheral surface with the peripheral surface of another roll.  
     [0024] The inking unit  6  of FIG. 1 contains, as an example, an inking fountain  14  and a roll train comprising inking rolls  16 - 27 , of which one roll  16  is what is known as a ductor roll for picking up ink from the ink fountain  14 , and of which at least one roll is driven by means of an electric motor, not shown, or another motor drive, and of which one or more rolls do not have any motor drive but only, by means of contact between their roll periphery with an adjacent roll, are driven by this adjacent roll, which can likewise be a roll without a motor drive.  
     [0025] A doctor  30  can be set against one of the inking rolls which is remote from the ductor roll  16 , in order to doctor off ink and other contaminants from this roll  27 , preferably into a holding trough  32 .  
     [0026] The damping unit  8  contains a damping solution trough  36 , from which, via a train of damping rolls  38 ,  39 ,  40  and  42 , damping solution liquid is applied to the circumferential surface of the plate cylinder  2  in order to form ink-repelling regions in accordance with the printing image to be printed.  
     [0027] According to a particular embodiment, a transfer roll  44  or a plurality of transfer rolls can be provided, which on one side is in circumferential contact with a damping roll, for example damping roll  42 , and on the other side is in circumferential contact with an inking roll, for example the inking rolls  26  and  27 . By means of such a combination, at the start of a printing operation, an optimum printing condition can more quickly be achieved on the plate cylinder  2 .  
     [0028] According to the invention, a printing unit roll cleaning apparatus  46  is provided for cleaning rotating rolls in a roll train, of which at least one roll can be driven by motor, for example the inking roll  17  after the ductor roll  16 , and of which at least one roll, for example 19, can be driven only by contact between its peripheral surface and the peripheral surface of one of the other rolls, and of which at least one roll is an inking roll for transferring ink. According to the example of FIG. 1, all the inking rolls  16 - 27  of the inking unit  6  and the transfer roll  44  are to be washed.  
     [0029] The cleaning apparatus  46  contains a liquid application apparatus  48 . This contains a distributor duct  49  having a large number of liquid discharge openings  50 , which are positioned or can be positioned along a first of the rolls, for example the inking roll  18 , which can be a motor-driven or a non-motor-driven roll, at a distance from said roll, in order to apply liquid to the peripheral surface of the roll  18 . As a result of rotation of this roll  18 , this liquid is transferred to the other rolls in peripheral contact with it and, from these rolls, also to further rolls in contact with them. The discharge openings  50  can be holes or nozzles inserted into holes.  
     [0030] “Liquid” can be solvent, detergent, water containing detergent or solvent, water with one or more additives which influence the printing process, pure water or any other liquid. Furthermore, the type of liquid can be changed during the washing operation. For example, at the start, detergent or solvent or water containing once can be used to loosen ink from the rolls, in order to be rinsed afterwards with clear water.  
     [0031] The liquid discharge openings  50  have a small size and shape, in such a way that liquid can be applied only to discrete longitudinal wetting zones  52  of this first roll  18 , leaving longitudinal non-wetting zones  54  between them on this first roll  18 . The width of a longitudinal wetting zone  52  is equal to the width of a liquid jet.  
     [0032] Furthermore, the cleaning apparatus  46  contains a liquid feed device  56  for feeding liquid to the discharge openings  50  and from the latter to the peripheral surface of the first roll  18  in such a quantity of liquid that, as a result of the rotation of the rolls, the liquid is transferred from the discrete wetting zones  52  of the first roll  18  to the peripheral surface of the further roll resting on its peripheral surface, the rolls  17  and  19  in the present example. As a result of the rotation of the rolls, the liquid is transferred from the longitudinal wetting zones  52  of the first roll  18  to longitudinal wetting zones lying opposite them on the at least one further roll  17  and  19 , leaving longitudinal non-wetting zones thereon. In the same way, the liquid is transferred to discrete longitudinal wetting zones  52  from roll to roll to further rolls, to the rolls  19 - 27  in the present example.  
     [0033] The liquid flows away further out from roll to roll on the rotating rolls in the roll longitudinal direction over the longitudinal wetting zones  52 , as illustrated schematically in FIG. 2 by “dot-dot-dash” lines  52 - 2 .  
     [0034] In this way, with each roll revolution, the liquid is distributed more and more to the longitudinal non-wetting zones  54  and therefore to the entire length of all the rolls  16 - 27  and  44  to be cleaned.  
     [0035] The quantity of liquid per unit time from the discharge openings  50  can be constant or variable.  
     [0036] The liquid jets are to strike the roll “gently”. Therefore, they are preferably applied to the surface of the roll periphery in the form of an arcuate jet. FIG. 1 shows the liquid jets  51  only schematically.  
     [0037]FIG. 1 shows, on the left, an application apparatus  48  whose liquid jets  51  are aimed at the roll  18  and, on the right, a further application apparatus  48 , which can be used alternatively or additionally, whose liquid jets  51  are aimed into the pocket between two rolls, for example the rolls  17  and  18 .  
     [0038] According to a preferred embodiment of the invention, the liquid discharge openings  50  are designed to generate liquid jets  51  which have a point-like cross section from the discharge openings  50  as far as the roll  17  or  18 .  
     [0039] At its lower end, the application apparatus  48  is preferably provided with a collecting trough  64  for collecting washing liquid that drips off, said trough  64  having a drain  66 .  
     [0040]FIG. 2 shows a possible embodiment of a liquid feed device  56 . Fresh water from a fresh water connection  74  can be fed to a detergent container  70  via a valve  72 . If desired, an automatic feed device for detergent or solvent  76  into the detergent container  70  can be provided. From the detergent container  70 , a line  78  which contains a pump  79  and a valve  80  goes to the distributor duct  49  of the liquid application apparatus  48 . Furthermore, a fresh water feed line  92  which contains a valve  93  can be provided from the fresh water connection  74  to the distributor duct  82 . Therefore, via all the discharge openings  50 , firstly washing liquid containing detergent or solvent or, secondly, fresh water can be fed in as desired. According to other embodiments of the liquid feed device  56 , only the feed of washing liquid containing detergent or solvent or only the feed of fresh water can be provided. The valves and pumps are controlled by means of an electronic control device  94 , preferably as a function of a higher-order machine operating program belonging to the press.  
     [0041] The invention is not restricted to offset presses but can also be used for cleaning inking rolls in other types of press.  
     [0042] Instead of a doctor  30 , another dirt wiping element can also be used, for example a cloth or a brush, which is placed on one of the rolls to be cleaned in order to wipe ink and washing liquid off it.