PRINTING GROUP FOR ROTOGRAVURE PRINTING PRESSES

Abstract: The invention falls within the sector of rotogravure printing presses and more precisely refers to the printing group (2) which is provided with a device (8) for adjusting a doctor (7) which acts on an impression cylinder (5). The adjusting device (8) is structured so as to be controlled by a processor on which the value of the diameter of the impression cylinder and the value of the working angle of the doctor on the cylinder are preset. The printing group (2) is completely enclosed between walls which create a space inside which nozzles (41, 42, 45 and 46) for washing the entire printing group and, in particular the doctor, are housed.

Description: PRINTING GROUP FOR ROTOGRAVURE PRINTING PRESSES DESCRIPTION The present invention relates to a printing group for rotogravure printing presses. Printing presses of the rotogravure type are provided with different printing stations, each of which is intended for a single colour. Each station comprises a printing group composed of a cylinder on which the image to be printed is etched and against which the continuous strip, onto which the image is to be transferred, is pressed by a pressure roller. The impression cylinder is inked by means of an inking roller partially immersed in an inking tray. A blade, known as a "doctor" in technical jargon, lightly presses against the impression cylinder so as to remove the excess ink and form a film of ink on the etched or engraved zone of the impression cylinder. Each printing group, which comprises, as is known, the impression cylinder, the inking roller and the doctor, is also provided with accessory elements such as a device for adjusting the correct position of the doctor and an ink collecting tray. During printing, the continuous strip on which the image is printed passes in succession between the impression cylinder and pressure roller of the various printing stations, in each of which one of the colours of the image to be printed is impressed onto the strip itself. Once a printing step has been completed, in order to start another one, with a different image, it is obviously necessary to change all the impression cylinders of the various stations. This operation requires a considerable amount of time since it is necessary to remove the impression cylinder from its seat, replace the impression cylinder with the next impression cylinder, change the ink in the inking devices, carefully wash all the parts which come into contact with the ink using potentially harmful solvents, and re-position correctly the impression cylinder with respect to the station, as well as the doctor with respect to the impression cylinder. All this must obviously be carried out for each printing station, employing several persons. It also also necessary to take into account the difficulties involved in performing this operation since the impression cylinder is of a considerable size and weight . During the aforementioned operation, the machine is obviously at a standstill for a period of time which depends on the number of printing groups and in any case is never less than one hour; this fact, in view of the considerable cost of rotogravure printing presses, results in a considerable increase in costs, which in practice makes the printing of small runs uneconomical and in any case has an effect on the cost of each run. In order to speed up the operations for replacement of the impression cylinders, for some time cylinder- carrying carriages have been used, said carriages supporting the cylinder and being inserted underneath the structure of the printing station so as to facilitate the operations for removal and insertion of the cylinder. It is common practice to use two of these carriages for each printing station: while one carriage remains in the press ready to extract the cylinder and if necessary the ink tray, the second carriage is already equipped with the new cylinder and the new tray so as to be able to be inserted underneath the printing station once the previous cylinder has been extracted. The cylinders used with the associated trays must then be carefully washed again using potentially harmful solvents. All this results in high operating costs as well as problems affecting the hygiene and health of the machine maintenance operators. The object of the present invention is that of reducing considerably the time required for replacement of the impression cylinder and of performing washing of the entire printing group and in particular the doctor, automatically, without the help of operators in order to avoid problems associated with the health of the operators themselves. A further object is that of performing always automatically all the necessary adjustments of the doctor depending on the extension of the impression cylinder and the angle of inclination of the doctor itself, by means of the action of a single operator who enters the aforementioned data on a processor. It has been found that with the device according to the present invention, the replacement times are reduced about tenfold compared to the times necessary with the known printing groups. These and other objects are all achieved with the printing group according to the present invention which is characterized by that contained in the claims indicated below. Characteristic features and advantages will emerge more clearly from the following description of a preferred embodiment illustrated purely by way of a non-limiting example in the accompanying plates of drawings in which: - Figure 1 shows a diagrammatic side view of a printing station; - Figures 2 and 3 show a plan view of the doctor with the associated device for adjusting the position with respect to the impression cylinder; - Figure 4 shows the doctor along the section III-III of Fig. 3; - Figure 5 shows a side view of the device for raising and inserting the impression cylinder; - Figure 6 shows a front view of the device according to Fig. 5; Figures 7, 8 and 9 show the system for washing the impression cylinder and the tray in two operating positions of the doctor. With reference to Figure 1, 1 denotes a printing station in a printing press of the rotogravure type, in which station there is provided, in the bottom zone, a printing group 2 above which a system of rollers 3 for conveying a continuous film 4 is positioned. The printing group comprises an impression cylinder 5 against which the continuous film 4 is pressed by means of a pressure roller 6. The impression cylinder is acted on by a doctor 7 supported by an adjusting device 8 which will be illustrated in greater detail below. Below the impression cylinder there is positioned an ink containing tray 9 housing an idle inking roller 10 kept pressed against the impression cylinder by two pneumatic cylinders 11 which support the entire tray by means of an intermediate frame 12. As can be seen from Figure 1, the entire printing station 1 is enclosed between metal walls inside a chamber (50) in which there are provided only two slits 13 and 14 for passage of the film 4, the rear wall being provided with an inspection and maintenance hatch 15. With reference to Figs. 2, 3 and 4, the device 8 for adjusting the doctor 7 will now be described. The doctor 7 is fixed by known means, which are not described here, onto a bar 16 which is able to rotate about a horizontal pivot 17 or perform a translatory movement vertically since the said bar is supported by two vertical columns 18 sliding in bushes 19 integral with the frame of the printing station; the two columns 18 are connected together at the bottom by means of a cross-piece 20. Each column has milled on it a rack 21 which meshes with a pinion 22 keyed onto a shaft 23 supported by two supports 24. The shaft 23 is driven by means of an electric motor 25 connected to a reducer 25a keyed onto said shaft. On the opposite side to the driving system, the shaft 23 has keyed onto it an encoder 26 designed to detect the number of revolutions of the shaft 23 itself. Two end-of-travel stops 27 and 28 determine the maximum travel or vertical displacement of the doctor-carrying bar 16. A pair of pneumatic cylinders 29, supported by the columns 18 and hence translating together with the columns themselves by means of two brackets 30, is provided for rotation of the bar 16 about the pivot 17. The rod of each cylinder 29 is connected to a ball joint 31 which is connected to the bar 16. The doctor adjusting device described above, via connection of the encoder and the electric motor to a processor, allows the position of the doctor to be adjusted automatically depending on the diameter of the impression cylinder; in short, the operator must simply set the diameter of the cylinder and the working angle of the doctor on the computer and automatically the electric motor will perform a predetermined number of rotations so as to bring the doctor into an optimum position, whereas the angular position is determined by the cylinders 29. The working angle of the doctor is chosen depending on various factors such as, for example, the quality of the inks, the incisions on the cylinder and the like. With reference to Figures 5 and 6, a device 34 for raising and inserting the impression cylinder 5 will now be described. 32 denotes a pneumatic cylinder with opposing rods, the rod 33 of which is connected to an arm 35a of a lever 35 pivotably mounted at 36. The rod 37 of the cylinder 32 is connected to the frame of the station and allows horizontal translation of the cylinder and the lever 35, while the rod 33 imparts a thrusting force to the impression cylinder (5) so as to push it out of the working position. For this purpose the lever 35 has an arm 35b which is inserted underneath the impression cylinder. During this phase, the impression cylinder 5 rolls on two horizontal guides 38 so as to end up on a carriage not illustrated. During unloading of the impression cylinder, the two rods 33 and 37 move out simultaneously so as to cause raising and thrusting of the impression cylinder. During loading of an impression cylinder, the lever 35 is arranged in the position shown in broken lines and indicated by (a) so as to prevent the impression cylinder from dropping suddenly onto the support rollers 39. Obviously there are provided two pneumatic cylinders 32 which operate two levers 35 located at the two ends of the impression cylinder. With reference to Figures 7, 8 and 9, the system for washing the printing group will now be described. With reference to Figure 1, it is possible to note the tray 9 supported by a frame 12 to which the hydraulic cylinders 11 are fixed. The washing system comprises a duct 40 located on the doctor side and having engaged on it a plurality of nozzles 41 with a jet directed substantially towards the point of contact of the doctor with the impression cylinder and a plurality of nozzles 42 with the jet directed towards a baffle 43 for guiding into the tray. Another duct 44 is positioned on the other side of the tray and has a plurality of nozzles 45 with the jet directed towards the impression cylinder and a plurality of nozzles 46 with the jet directed towards the walls of the tray. Figure 9 shows in broken lines the position of the tray 9 in the lowered position. The ducts 40 and 44 are able to rotate about their longitudinal axis so as to adapt to the different positions and orientations of the doctor upon variation in the diameter of the impression cylinder. All the improvements described above, relating to encasement of the printing station, the doctor adjusting device, the impression cylinder gripping and raising device, introduction of the system for washing the printing group and in particular the doctor, combine to ensure automation of all the operations necessary for changing the impression cylinder and changing the ink colour or type, with the advantage of reducing considerably the downtime for said replacement operations and reducing the atmospheric pollution of the solvents in the operating zone of the rotogravure printing press.

Claims: CLAIMS 1. Printing group for a rotogravure printing press of the type comprising an impression cylinder which is inked by an inking roller partially immersed in an inking tray, and a doctor which lightly presses against the impression cylinder in order to remove the excess ink, characterized in that the printing group is completely enclosed between walls inside a chamber (50) in which there are provided only slits (13) and (14) for passage of the film to be printed and comprises: a device (8) for' adjusting the position of the doctor (7) with respect to the impression cylinder (5) which allows automatically the displacement in a vertical plane and rotation of the doctor depending on the value of the diameter of the impression cylinder and the working angle of the doctor on the impression cylinder. 2. Printing group according to Claim 1, characterized in that the device (8) for adjusting the position of the doctor (7) comprises a doctor-carrying bar (16) supported by columns (18) performing a translatory movement in a vertical plane and rotating about a horizontal pivot (17); a motor-driven shaft (23) kinematically coupled to the columns (18) for translation in a vertical plane of the columns themselves; pneumatic cylinders (29) supported by the columns (18) and with the associated rod acting on the bar (16); an encoder (26) which is keyed onto the shaft (23) and which sends the signals to a processor which causes rotation of the shaft (23) and energising of the pneumatic cylinders (29) depending on the diameter of the impression cylinder and the working angle of the doctor which are preset on the processor itself. 3. Printing group according to Claim 1, characterized in that it comprises, inside the chamber (50) in which the printing group is enclosed, a plurality of nozzles (41) having a jet directed substantially towards the point of contact of the doctor with the impression cylinder and designed to spray washing solvent which is collected by the inking tray. 4. Printing group according to Claim 1, characterized in that it comprises a device (34) for raising and inserting the impression cylinder (5), consisting of two levers (35) each of which has an arm (35a) actuated by a pneumatic cylinder (32) with opposing rods and an arm (35b) which is inserted underneath the impression cylinder so as to cause raising thereof and subsequently pushing towards horizontal unloading and loading guides (38) . 5. Printing group according to Claim 4, characterized in that the nozzles (41) can be oriented depending on the position assumed by the doctor.

Inventors: BOSONI GIANNINO, BOSONI, GIANNINO
Applicants: BOSONI GIANNINO, SCHIAVI SPA, BOSONI, GIANNINO, SCHIAVI S.P.A.
Application year: 1997
Main classification: B41F9
IPC codes: B41F9, B41F13, B41F31, B41F35