Abstract:
A printing-machine cylinder includes a basic cylinder body and a covering element fitted to the basic cylinder body, one of the basic cylinder body and the covering element being formed with a multiplicity of recesses connectable to one of a suction-air source and a blast-air source and having, in the region of the recesses, through-channels extending from the recesses to the peripheral surface of the covering element and defining blasting/suction sections for acting upon the underside of a sheet conveyed on the peripheral surface of the cylinder; a printing machine Including the cylinder; and a method for producing the cylinder.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a printing-machine cylinder, especially an impression cylinder, for a sheet-fed rotary printing machine, and to a method for producing such a printing-machine cylinder. 
     When sheets are being transported through a sheet-fed rotary printing machine, they are printed in a conventional manner in a printing nip formed between an impression cylinder and an associated blanket cylinder, and are then fed, by one or more transfer cylinders, to a downstream printing unit or a reversing or turning device. In order to prevent smearing of the freshly printed side of the sheet on the transfer cylinders, it has become known heretofore to provide openings in the peripheral surface of the cylinders, through which blast air is blown for carrying the sheets on the peripheral surface of the transfer cylinders without smearing. 
     Both in the case of the sheet transfer cylinders described above and in the case of impression cylinders of sheet-fed rotary printing machines which are assigned to a reversing device, and in which, during first-form and perfecting operation, the sheets are carried on the upline impression cylinder and the trailing edge of the sheets is accepted by a gripper device of the downline transfer cylinder, it has become known heretofore to suck the sheet onto the peripheral surface of the cylinder in order to hold it on the peripheral surface. 
     The published non-prosecuted German Patent Application (DE-OS) 41 26 643 A1 discloses a transfer cylinder for a sheet-fed rotary printing machine having a basic cylinder body formed by four supporting disks whereon a total of three supporting elements are fastened. Each of the supporting elements has a sandwich-like construction, at the center of which, suction chambers are defined by a metal sheet folded in a serpentine manner and covered towards the outside of the cylinder by a sheet-metal covering having a thin wall and curved so as to correspond to the curvature of the cylinder. Each of the chambers has a flow connection to the environment via associated openings in the sheet-metal covering, and can have suction air applied thereto via a rotary valve, in order to suck a sheet onto the peripheral surface of the cylinder and smoothen it. Because of the thin-walled folded metal sheet used to form the chambers, and the associated sandwich-like construction of the cylinder, the latter is not suitable for use as an impression cylinder in a printing unit of a sheet-fed rotary printing machine. 
     The published European Patent Document EP 0 165 477 B1 has disclosed a sheet-fed rotary printing machine with a reversing or turning device having an impression cylinder arranged upline of the reversing device and onto which the sheets to be reversed or turned are sucked and held. The impression cylinder has a solid basic body, in which suction-air or blast-air feed channels, which extend axially over the entire width of the cylinder, are formed. From each of the feed channels, a multiplicity of radial holes or bores extend to the peripheral surface of the basic cylinder body. In addition, a textured film is drawn onto the peripheral surface of the basic cylinder body and, in the region of the radial bores, is porous or is formed with openings through which a sheet transported on the cylinder can be sucked against the peripheral surface and lifted off the latter, respectively. From this published. European patent document, it is also known to provide a transfer cylinder, that is constructed as a storage drum and is covered with a porous film, with a suction box that can be moved so as to adapt it to different sheet formats and that sucks the trailing edge of a sheet to be reversed or turned, against and onto the peripheral surface of the transfer cylinder. Because of the feed holes, which extend in the axial direction over the entire width of the impression cylinder, and the numerous fine radial holes or bores to be introduced into the peripheral surface of the basic body of the impression cylinder, the production of the described impression cylinder proves to be extremely complicated and costly. 
     Because of the comb-like or finger-like configuration of the peripheral surface of the transfer cylinder, that is associated with the ability of the suction box to be moved, the transfer cylinder is not suitable likewise for use as an impression cylinder in a sheet-fed rotary printing machine, because the comb-like structure of the peripheral surface is transferred to the printed image and has a lasting detrimental effect upon the latter. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a printing-machine cylinder, especially an impression cylinder for a sheet-fed rotary printing machine, that is simple and inexpensive to produce and that permits sheets carried on the cylinder to be both sucked onto it and blown off it. 
     Furthermore, it is an object of the invention to provide a production method by which a printing-machine cylinder, especially an impression cylinder of a sheet-fed rotary printing machine that has a peripheral surface provided with blast or suction openings, can be produced in a simple and more cost-effective manner. 
     With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a printing-machine cylinder comprising a basic cylinder body and a covering element fitted to the basic cylinder body, one of the basic cylinder body and the covering element being formed with a multiplicity of recesses connectable to one of a suction-air source and a blast-air source and having, in the region of the recesses, through-channels extending from the recesses to the peripheral surface of the covering element and defining blasting/suction sections for acting upon the underside of a sheet conveyed on the peripheral surface of the cylinder. 
     In accordance with another aspect of the invention, there is provided a printing-machine cylinder comprising a basic cylinder body having a multiplicity of recesses formed therein and being connectable to one of a suction-air source and a blasting-air source, and having a covering element fitted to the basic cylinder body and, in the region of the recesses, being formed with through-channels extending from the recesses to the peripheral surface of the covering element and defining blasting/suction sections for acting upon the underside of a sheet being conveyed on the peripheral surface of the cylinder. 
     In accordance with a further aspect of the invention, there is provided a printing-machine cylinder comprising a basic cylinder body, and a covering element fitted to the basic cylinder body and formed on the inside thereof with a multiplicity of recesses connectable to one of a suction-air source and a blast-air source and, in the region of the recesses, being formed with through-channels extending from the recesses to the peripheral surface of the covering element, and defining blasting/suction sections for acting upon the underside of a sheet conveyed on the peripheral surface of the cylinder. 
     In accordance with another feature of the invention, the through-channels have a section of relatively larger diameter and a section of relatively smaller diameter. 
     In accordance with a further feature of the invention, the section of relatively larger diameter is formed as a bore in the covering element and extends in a direction from the center of the cylinder. 
     In accordance with an added feature of the invention, the blasting/suction sections are arranged substantially in rows on the peripheral surface of the cylinder. 
     In accordance with an additional feature of the invention, the rows extend substantially parallel to one another. 
     In accordance with yet another feature of the invention, the rows extend in the axial direction. 
     In accordance with yet a further feature of the invention, as viewed in the direction of rotation of the cylinder, the rows are of decreasing length. 
     In accordance with an added feature of the invention, the rows extend in the peripheral direction. 
     In accordance with yet an additional feature of the invention, the rows extend substantially in a V-shape or ray shape. 
     In accordance with still another feature of the invention, the printing-machine cylinder includes a connecting line for applying one of suction air and blasting air in common to the recesses assigned to a row. 
     In accordance with still a further feature of the invention, the printing-machine cylinder includes valves assigned to the recesses for connecting the recesses, individually or in groups, to the one of the suction-air source and the blasting-air source. 
     In accordance with still an added feature of the invention, the recesses are subjectible to the application of said one of suction air and blast air depending upon the sheet format to be processed, in a manner that only the blasting/suction sections underneath a sheet conveyed on the cylinder have the one of suction air and blast air applied thereto. 
     In accordance with still an additional feature of the invention, the printing-machine cylinder includes a control device for controlling a feeding of the one of suction air and blast air to the recesses. 
     In accordance with another feature of the invention, all of the recesses are connectable simultaneously to the one of the suction-air and blast-air sources via the control device. 
     In accordance worth a further feature of the invention, the through-channels in the covering element have a cross section widening in a direction towards the recesses. 
     In accordance with an added feature of the invention, the peripheral surface of the covering element has a porous film applied thereto, wherein those sections of the through-channels which have a relatively smaller diameter are formed. 
     In accordance with an additional aspect of the invention, there is provided a printing machine having the cylinder that is formed as an impression cylinder arranged upline of a reversing device, the control device, during first-form and perfecting operation, serving to connect the recesses, in a region between a printing nip and a transfer center line between the impression cylinder and a downline sheet-carrying cylinder, to the suction-air source, in order to hold the sheets on the peripheral surface of the cylinder. 
     In accordance with another feature of the invention, the control device, during first-form and perfecting operation, serves to connect the recesses, in a transfer region that as one of directly upstream and directly downstream of the transfer center line and wherein a trailing edge of the sheet is acceptable by a gripper device of a downline sheet-carrying cylinder, to the blast-air source. 
     In accordance with a further aspect of the invention, there is provided a printing-machine cylinder comprising a basic cylinder body and an air-permeable, porous covering element fitted to the basic cylinder body and having a multiplicity of interconnected channels formed therein, the channels being connectable to one of a suction-air source and a blast-air source via air feed lines for sucking a sheet carried on the cylinder onto the peripheral surface of the cylinder or for lifting the sheet off the peripheral surface of the cylinder. 
     In accordance with an added feature of the invention, the air feed lines are formed in the basic cylinder body. 
     In accordance with an additional feature of the invention, as viewed in the direction of rotation of the cylinder, during first-form and perfecting operation, the control device serves to connect the recesses, in the region between a transfer center line between the cylinder and a downline sheet-conveying cylinder and a printing nip, to the blast-air source, so as to detach the sheets from the peripheral surface of the cylinder. 
     In accordance with yet another aspect of the invention, there is provided a method for producing a printing-machine cylinder, which comprises the steps of making a basic cylinder body ready; forming recesses in a peripheral surface of the basic body; introducing at least one air-supply bore into the recesses; fitting a cylinder covering element to the basic cylinder body, the cylinder covering element having, in the region of the recesses, a multiplicity of through-channels extending from the recesses to the peripheral surface of the cylinder covering element. 
     In accordance with yet an added aspect of the invention, there is provided a method for producing a printing-machine cylinder, which comprises the steps of making a basic cylinder body ready; making a cylinder covering element ready; forming recesses in the inside of the cylinder covering element; introducing into the cylinder covering element a multiplicity of through-channels, extending from the recesses to the peripheral surface of the cylinder covering element; forming at least one air-supply bore in the basic cylinder body; and fitting the cylinder covering element to the basic cylinder body. 
     In accordance with another mode, the method of the invention includes the further step of applying a porous film or foil to the peripheral surface. 
     In accordance with an additional aspect of the invention, there is provided a method for producing a printing-machine cylinder, which comprises the steps of providing a basic cylinder body; introducing an air-feed line into the peripheral surface of the basic cylinder body; and fitting a porous, air-permeable cylinder covering element to the basic cylinder body. 
     In accordance with another feature and mode of the cylinder and the method of the invention, the cylinder is an impression cylinder for a sheet-fed rotary printing machine. 
     In accordance with a concomitant feature of the printing machine of the invention, the printing machine is a sheet-fed rotary printing machine, and the cylinder is an impression cylinder. 
     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 printing-machine cylinder, especially an impression cylinder, for a sheet-fed rotary printing machine, and a method of production thereof, 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 DRAWINGS 
     FIG. 1 is a fragmentary diagrammatic side elevational view of a sheet-fed rotary printing machine having a printing-machine cylinder according to the invention, that is formed as an impression cylinder, disposed upline of a reversing or turning device; 
     FIGS. 2A and 2B are fragmentary diagrammatic longitudinal sectional views of the outer surface of a first embodiment of a printing-machine cylinder according to the invention, wherein both through-channels and fine openings arranged above the latter are formed directly in a covering element of the cylinder, in FIG. 2A recesses and distribution chambers are formed in a basic body, in FIG. 2B recesses and distribution chambers are formed in a covering element of the cylinder; 
     FIGS. 3A and 3B are fragmentary diagrammatic longitudinal sectional views of another embodiment of a printing-machine cylinder according to the invention, wherein through-channels are formed in the covering element of the printing-machine cylinder and are covered by a porous film stretched over the peripheral surface of the covering element, in FIG. 3A recesses and distribution chambers are formed in a basic body, in FIG. 3B recesses and distribution chambers are formed in a covering element of the cylinder; 
     FIGS. 4A and 4B are fragmentary diagrammatic longitudinal sectional views of a further embodiment of a printing-machine cylinder according to the invention, wherein through-channels in the covering element have a cross section widening towards the center of the cylinder, in FIG. 4A recesses and distribution chambers are formed in a basic body, in FIG. 4B recesses and distribution chambers are formed in a covering element of the cylinder; 
     FIGS. 5A and 5B are diagrammatic and schematic side elevational views, partly in section, of an embodiment of a printing-machine cylinder according to the invention, wherein the blast/suction regions are arranged in rows on the peripheral surface of the cylinder, in FIG. 5A the rows are parallel to each other, in FIG. 5B the rows are arranged in a V-shape configuration; and 
     FIG. 6 is a fragmentary diagrammatic longitudinal sectional view of yet another embodiment of a printing-machine cylinder according to the invention, wherein the cylinder covering is produced from a porous, air-permeable material. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and, first, particularly to FIG. 1 thereof, there is diagrammatically illustrated therein a printing-machine cylinder  1  according to the invention that is preferably an impression cylinder cooperating with an associated blanket cylinder  2 , in a printing unit  4  of a sheet-fed rotary printing machine. The cylinder  1  has a basic body  8  which, in the preferred embodiment of the invention, is formed as a casting provided with cavities  6  and ribs  10 , for example, a casting made of gray cast iron. As is further illustrated in FIG. 1, the printing-machine cylinder  1  according to the invention is preferably used in a printing unit  4  arranged upline of a reversing or turning device  12 . The reversing device  12  is indicated diagrammatically in FIG. 1 by a reversing or turning drum  14  having an otherwise unidentified suction gripper and an accepting or take-over gripper. In the same way, however, it is also possible to use the printing-machine cylinder  1  according to the invention as a transfer cylinder arranged between two printing units of a sheet-fed rotary printing machine, on the peripheral surface of which the sheets  16  freshly printed in the preceding printing unit are carried without smearing by using blast or blown air or, if required, or example during perfecting operation, are sucked onto the peripheral surface in order to smoothen the sheets  16 . 
     As is illustrated in the enlarged sectional views of the basic body  8  of the printing-machine cylinder  1  according to the invention in FIGS. 2A,  3 A and  4 A, recesses  20  are machined in the basic body  8 , it being possible, for example, for the recesses  20  to be milled into the basic body  8  in the course of a rough machining of the latter after it has been cast. In a similar manner, however, provision may also be made for the basic structure of the recesses  20  to be provided in the peripheral surface of the basic body  8  during casting, and for these then to be subsequently machined as necessary or desirable. 
     The recesses  20  define air distribution chambers  26 , which are connectable via an air feed line  28  to an otherwise non-illustrated blast-air or suction-air source, it being possible for the flow connection between the blast-air or suction-air source and the air distribution chambers  26  to be made preferably via one or more valves  30 , illustrated diagrammatically as a block in FIG. 1, and a control device  32 , in the form of a conventional rotary lead-through or a rotary valve. 
     After the machining of the basic cylinder body  8 , a solid covering element  17  is fitted to the peripheral surface of the latter, for example, pushed or slid on axially. The covering element  17  may have a thickness of approximately 10 mm, for example, and is formed in the vicinity of the recesses  20  with through-channels  24  which define blasting/suction regions or sections  22  on the peripheral surface  18  of the cylinder  1 . 
     In the embodiment of the invention illustrated in FIGS. 2A and 2B, each of the through-channels  24  (not shown in FIG. 2B) has a channel section  24   a  (not shown in FIG. 2B) of larger diameter formed in the covering element  17  from the center of the cylinder  1 , as well as a number of sections  24   b  which are arranged above and communicate with the section  24   a  and have a diameter that is several times smaller. The diameter of the channel sections  24   a  may, for example, be in the range between 0.5 mm and 1.5 mm, while the diameter of the channel sections  24   b  may be in the range from 0.05 to 0.2 mm. 
     With regard to the further embodiment of a printing-machine cylinder  1  according to the invention illustrated in FIGS. 3A and 3B, a porous film or foil  34  can be applied to the outer peripheral surface of the covering element  17 , the channel sections of smaller diameter  24   b  being formed in this film or foil  34 , for example, by a laser or by etching, and so forth. Porous textured films or foils, for example, in the form of glass-bead blankets or so-called textured chromium coverings have become known heretofore, for example, from the European Patent 0 165 477. The film or foil  34  can, for example, be stretched onto the peripheral surface  18  of the covering element  17  or else adhesively bonded thereon and is used to distribute the impression pressures, which act in the printing nip when a cylinder  1  according to the invention is used as an impression cylinder, uniformly in the region of the through-channels  24  (not shown in FIG.  3 B), in order to avoid the occurrence of offprints or reproductions in the printed image due to the channels  24 . 
     As is shown in FIGS. 4A and 4B, in an embodiment of the invention that likewise uses a porous film or foil  34 , provision may furthermore be made for the channel sections  24   a  of the through-channels  24  (not shown in FIG. 4B) to have a cross section that widens in the direction of the air distribution chamber  26 , it being possible for the cross section of the through-channels  24  in the region of the air distribution chambers  26  to be twice as large, for example, as the cross section at the opposite end of the through-channels  24 . In the case of suction-air operation of the printing-machine cylinder  1 , this results in a considerably reduced susceptibility to failure with respect to blockages, which can be caused, for example, by the penetration of paper dust or other particles into the through-channels  24 . 
     The production of the covering element  17  with the through-channels  24  arranged therein is advantageously performed independently of the machining of the basic cylinder body  8 . The multiplicity of through-channels  24  may thereby be introduced into the peripheral surface  18  of the covering element  17 , for example, with the aid of suitable tools, such as batteries of drills or laser machining tools, which results in considerable advantages from a production point of view. Thus, because of the separate machining, in the event of breakage of a drilling tool during the drilling of the through-channels  24 , for example, no damage occurs to the basic cylinder body  8 , which is considerably more complicated to produce, as is the case, for example, during the production of printing-machine cylinders in accordance with the prior art, wherein the channels are generally introduced directly into the peripheral surface of the unipartite cylinder body. Furthermore, the machining time is reduced considerably by the separate machining of the covering element  17  and the basic cylinder body  8 , because some of the successively performed machining steps in the case of unipartite cylinders can then be performed simultaneously on different machining devices. 
     After the cylinder covering element has been produced in the manner described hereinbefore, preferably by machining a flat metal plate, it is applied to the peripheral surface of the roughly prepared basic cylinder body  8  and affixed to the latter, for example, by being screwed from the inside or by being adhesively bonded or welded. In this regard, provision may be made for he covering element  17  to be provided beforehand with a permanent curvature corresponding to the curvature of the outer peripheral surface of the basic cylinder body  8 , for example, by a plastic deformation process, so that the covering element  17  is held in a substantially stress-free manner on the basic cylinder body  8 . Provision can also be made for the covering element  17  to be provided beforehand with a more pronounced curvature than the cylinder curvature, so that after the covering element  17  has been applied to the basic cylinder body  8 , it is prestressed in the outer regions. 
     In a further step, a fine machining of the peripheral surface of the covering element  17  fitted to the basic cylinder body  8  can, if necessary or desirable, then take place, by which irregularities in the roundness of the cylinder, which generally lead to a disadvantageous impairment of the printed image, are eliminated. 
     As is illustrated in FIGS. 5A and 5B, in the preferred embodiment of the invention, the recesses  20  are formed in the peripheral surface of the basic cylinder body  8  as grooves  20   a , the blasting/suction sections  22  having the form of strips. In this regard, a number of air distribution chambers  26 , to which blast air or suction air can be applied separately from one another, are preferably arranged along one of the groove-like recesses  20   a . The grooves  20   a  can extend both in the peripheral direction and in the axial direction along the peripheral surface  18  of the printing-machine cylinder  1 . As is further shown in FIG. 5A, the blasting/suction sections  22  on the peripheral surface  18  of the cylinder  1  are preferably arranged in parallel rows  40 , which can extend both in the peripheral direction and in the axial direction over the peripheral surface  18 . In the same manner, as shown in FIG. 5B, provision can also be made for the rows  40  to run in a substantially V-shape or ray shape on the peripheral surface  18  of the cylinder  1 . This can be achieved, for example, by the rows  40  extending in the axial direction, as viewed in the direction of rotation  42  of the cylinder  1 , having a decreasing length, as a result of which, in the case of a sheet  16   a  of small format, only the blasting/suction sections  22  in the region of the sheet trailing edge  44   a  in the center of the peripheral surface  18  of the cylinder  1  apply suction to the small-format sheet  16   a . During the processing of large-format sheets  16   b , which generally have a greater weight and are therefore subject to the action of a greater centrifugal force, by contrast preferably all the blasting/suction sections  22  on the peripheral surface  18  are activated to apply suction air or blast air to the sheets  16 , so that large-format sheets  16   b  are held on the peripheral surface  18  over virtually the entire area thereof and not just in the region of the sheet trailing edge  44   b  thereof. 
     As is indicated by the valves of the valve block  30  in FIGS. 5A and 5B, the blasting/suction sections  22  of the axial rows  40 , or the air distribution chambers  26  thereof, can preferably have blast air or suction air applied thereto in groups, the application being performed in dependence upon the sheet format to be processed, in such a manner that blast air or suction air is applied only to those sections  22  underneath a sheet  16  conveyed on the cylinder. In such an embodiment of the invention, preferably all of the sections  22  and the air, distribution chambers  26  thereof, respectively, are connected simultaneously to the suction-air or blast-air source, via the valve block  30  and via the control device  32  in the form of a conventional rotary lead-through. 
     In the same manner, provision can be made for the axial rows  40 , as viewed in the peripheral direction, to have suction air applied thereto progressively via the control device  32  after the printing nip has been passed, or shortly beforehand, so that the transported sheets  16  are sucked progressively onto the peripheral surface  18  of the cylinder  1  and are smoothened. In the same manner, the rows  40  of blasting/suction sections  22  can have blast air or blast-air pulses applied thereto progressively from a specific, predefined rotational-angle position, in order to detach the sheets  16  from the peripheral surface  18  or to clean the channels  24  of contaminants. 
     Especially when the printing-machine cylinder  1  according to the invention is used as an impression cylinder in a printing unit arranged upstream of a reversing or turning device, it has proven to be advantageous to apply suction air to the sections  22  arranged along an axial row  40 , or the distribution chambers  26  thereof, in the region between the printing nip and the transfer center line  46  to the downline reversing or turning drum  14  (FIG.  1 ), and to apply blast air to the corresponding axial rows  40  underneath the sheet trailing edge  44   a ,  44   b  only directly before and directly after, respectively, the sheet trailing edge  44   a ,  44   b  has been gripped by a gripper device of the reversing or turning drum  14 , in order to detach the sheet  16  sucked onto the peripheral surface  18  from the latter. 
     Furthermore, the possibility exists of forming the recesses  20  and distribution chambers  26  directly on the inside of the cylinder covering element  17  and of introducing only the suction holes  28  into the basic cylinder body  8 , as is shown in FIGS. 2D to  4 B. 
     According to a further embodiment of the invention, which is illustrated in FIG.  6  and in which parts corresponding to those in the preceding figures are identified by a reference numeral increased by  100 , the cylinder covering element  117 , that is fitted on the basic cylinder body  108  having air feed lines  128  formed therein, is formed from porous material. The material of the porous covering element  117  may be, for example, metal, ceramic or also plastic, it being possible for the microscopically small connecting channels  124  contained in the porous material of the cylinder cover  117  to be produced, for example, by etching or by sintering or in some other conventional manner. The connecting channels  124  are preferably also interconnected in the transverse direction and connect the peripheral surface  118  of the cylinder  1  to the air feed channels  128  in the basic cylinder body  108  in such a way that a sheet  16  carried on the cylinder  1  is preferably sucked onto the peripheral surface  118  over the entire area during suction-air operation and is lifted off the cylinder peripheral surface  118  during blast-air operation. 
     In the same manner as for the blasting/suction sections  22  of the aforedescribed embodiments of FIGS. 2,  3  and  4 , the air feed channels  128  of the embodiment shown in FIG. 6 can likewise be arranged along rows (not shown), and can have blast air or suction air applied thereto, region by region, via control devices, for example, rotary valves  32  (FIG.  1 ).