FR2784470A1 - Offset plate mounting for printing cylinder has grooved cylinder with vacuum source to clamp plate against cylinder - Google Patents

Abstract

The offset plate mounting for a printing cylinder uses a grooved cylinder (2) to receive the plate (1) which is covered at its ends by strips (3,4). The cylinder has openings (7) through which a vacuum is applied to grip the strips to the cylinder surface. An edge seal (6) forms a closed volume with the plate and cylinder surface to form a vacuum chamber.

Description

 The present invention relates to a device which makes it possible to fix by vacuum a flexible plate of indifferent format on a hollow cylinder subjected to vacuum and driven in rotation in order to engrave it (or to insulate it).

 It relates particularly but not exclusively to the engraving machines (flashing machines) called "external drum" which are mainly used to engrave large format offset plates (up to twenty four pages).

 With the devices known to date, the plate is held on the cylinder by mechanical means (with or without the addition of vacuum) which come to grip its two ends to ensure its good performance as well as its tension.

 These complex devices are very expensive in machining because the cylinder which must receive mechanical elements is very worked, and in addition, they only allow two or three different formats to be fixed on the cylinder, which is very disadvantageous.

 One result which the invention aims to obtain is such a device which ensures that a plate can be fixed to the same cylinder, whatever its format, by means of a simpler device and therefore less expensive than all those used for this purpose. day.

. 11 in fact comprises, according to a first characteristic, a cylinder on which will be
machined over its entire length circumferential external grooves, parallel and distant between them of about two centimeters and whose profile will be characterized by a very shallow depth (0.05 to 0.1 mm), a width of about 5 mm and will not have a sharp corner. This profile can therefore be perfectly matched by a flexible material of the foam or rubber type. This cylinder can be made of steel or aluminum and in all cases it must have a very good external surface condition (rectification) in order to ensure perfect contact with the plate. It will also have perfect geometry (the maximum defect in concentricity and in parallelism tolerated will be 0.02mm). We will apply a surface treatment to harden it surface (hard anodizing if the cylinder is aluminum or hard chrome if it is steel).

 A second characteristic consists in making the vacuum communicate between the inside of the cylinder (connected to the vacuum source) and the outside by a series of small diameter holes which will open out in the bottom of the grooves and will be arranged on or (around ) from a single generator of the cylinder.

 A third characteristic consists in clamping the head and the tail of the plate by removable flanges. These flanges will be applied to the cylinder when loading the plate and then removed to unload it. Their handling system will be fully automated and designed so that the grip of the flanges will be reset at each cycle by feet and conical positioning guns. The gripping of the flanges will be done by two electromagnets whose attraction force will be at least 80 DaN.

These briis will be coated on their periphery with a very soft foam or rubber seal (15 to 20 shores).

When loading, they will be applied "horse" on the ends of the plate and on the cylinder. Pressure will be applied to them so that the rubber seal perfectly matches the grooved profile of the cylinder and the contour of the plate. A series of rubber studs (or a leaf spring) arranged in the axis of the flanges and applied to the ends of the plate will prevent them from straightening.

 The fourth characteristic concerns the design of the flanges. I1 is indeed necessary that we can lock them mechanically so as to keep them in place on the cylinder before it is evacuated during loading and unloading cycles of the plate while keeping the seal slightly crushed. For this purpose, I therefore at each end of the flanges designed a locking system actuated by a micro jack (or an electromagnet) integral with the flange handling system. This lock, once closed, will be held in its position by a leaf spring which will exert on it a minimum pressure of 10 DaN. Furthermore, this device will act as safety in the event of a vacuum cut during operation.

An embodiment of the invention will be described below, by way of nonlimiting example, with reference to the appended drawings in which:
Figure 1 shows the cylinder and its clamping device in perspective (without the locking system).

Figure 2 shows the clamping device with its locking system.

FIG. 3 represents the cylinder seen in plan and in section.

Figure 4 shows the flange seen in plan from the side trimmed by the seals.

Figure 5 shows the entire device in phase (1) loading.

FIG. 6 represents the entire device in the loading phase (3).

Figure 7 shows the entire device at the end of loading.

FIG. 8 represents the additional device for positioning the flanges at the time of fitting or removing a flange.

With reference to FIG. 1, it can be seen that the device comprises a cylinder (2) which may be made of aluminum or preferably steel and whose circumferential external surface will be rectified and then will receive a surface treatment to harden it (hard anodic oxidation if the cylinder is aluminum or hard chrome if the cylinder is steel) and two flanges (a head flange (3) and a tail flange (4) made of aluminum. These flanges which will be fitted with a flexible seal (6) are removable. Their length will be the length of the cylinder, about five centimeters wide and
15 mm thick. They will be positioned on the cylinder by an additional electro-mechanical system that will be seen in Figure 8. The cylinder has a series of grooves (5) of about five millimeters in width and five to ten hundredths of a millimeter in depth obtained by rectification and a series of holes (7) whose diameter will be about one millimeter.

 Referring to Figure 2, we can see in section the flanges (3) and (4), the lock (9) which will be made of steel with its spring leaf (11), the pressure studs (20) made of rubber and the peripheral seal (6) which will be five to ten millimeters in width and about five millimeters in thickness. The centering barrel (19) made of hard steel and the gripping plate (17) made of steel which appear in this figure will be better explained by FIG. 8.

 Referring to Figure 3, we see the cylinder (2) with its series of grooves (5) and its row of holes (7) arranged on (or near) a single generator (8). We will also see on section AA of the cylinder the profile of a groove (7) and the location of the holes (5) which will preferably open but not necessarily in the axis of these grooves.

 Referring to Figure 4, we see in a plan view the arrangement of the seal (6) and the studs (20) under the flanges (3) and (4). The seal must perfectly "loop" to form after its application on the cylinder and on the end of the plate a sealed chamber.

 With reference to Figures 5,6 and 7 I will explain the progress of a loading cycle which will be carried out as follows.

 1) position the head of the plate (l) under the head flange (3) and above the row of holes (7). At this time, the head flange (3), the tail flange (4) and the pressure roller (10) are eclipsed (Figure 5).

 2) press the head flange (3) straddling the head of the plate and on the cylinder then lock it with the latches (9) by eclipsing the rod of the micro-jack (16).

 3) rotate the cylinder by an angle (â) to bring the head flange (3) just beyond a pressure roller (10). see figure 6.

 4) press the pressure roller (10). This will remain applied during the entire winding operation of the plate.

 5) continue rotation until the tail of the plate is positioned under the tail flange (4).

 6) press the tail flange (4) astride the tail of the plate and the cylinder. see figure 7.

 7) create a vacuum throughout the system.

 9) eclipse the pressure roller (10).

Note: before the system is put into rotation, the vacuum level will be checked, which will be at least 300 millibars.

 Referring to Figure 8, I will give a description of an automatic flange handling system. (The attached system may include all kinds of modifications). It consists of a steel profile beam (12) of square (or rectangular) section actuated by one (or two) pneumatic cylinder (13) in a linear movement of short stroke guided by two ball guide columns ( 14).

The clamps are taken by two electromagnets (15) whose attraction force will be at least 80 DaN and which will stick to the flanges thanks to the steel plates (17) which are fixed on their top. The loading (3) and unloading (4) clamps are reset in position during each cycle at the time of unloading thanks to the two conical positioning feet (18) integral with the beam (12) which will be indexed in the two conical barrels (19) fixed on the flanges (3 and 4). During this operation, it will be necessary to release the cylinder from its traction (de-energization) so that any angular catching up can be done without forcing.

 The locks (9) will be actuated for the locking and unlocking operation by 2 pneumatic micro-cylinders (16) or 2 electromagnets. To prevent the head and tail of the plates from tending to straighten, a flexible pressure device will be added under the flanges and in their axis, which may consist of a series of conical rubber pads (20) the base diameter of which will be approximately ten millimeters and the thickness of five millimeters. It could also be a series of springs, or a leaf spring.

Claims (6)

 1) Device for fixing by vacuum a flexible plate (1) of indifferent format on the circumferential external surface of a vacuum-tight cylinder (2), the interior of which is connected to a vacuum source, which comprises on its entire length a series of circumferential external grooves (5) of very shallow depth (a few hundredths) and a few millimeters in width, which will be pierced with a series of holes (7) arranged on (or near) a single generator (8) which should be positioned during the initial loading phase (illustrated in Figure 5) at the head of the plate, under the head flange (3) and which will make the inside communicate with the outside of the cylinder so that there is a vacuum under the head flange (3) then propagates to the tail flange (4) flowing through the groove sectors (5) located under the plate (1 ) characterized in that this propagation of the vacuum by the sectors of external grooves (5) to the cylinder (2) and located under the plate (1) will cause the positioning of the flange (4) which fixes the tail of the plate to depend only on the length of this plate which will have at most the circumferential length of the cylinder minus the length of the sector of this cylinder necessary for positioning the head (3) and tail (4) flanges thus, knowing that its width can be arbitrary provided that it does not exceed the grooved useful length of the cylinder (2), we see that it will be possible to fix on this cylinder any format of plates whose maximum dimensions will meet the criteria if stated above.  2) Device according to claim 1 characterized in that the head and the tail of the plate will be maintained by two flanges (3) and (4) removable equipped on their part coming into contact with the cylinder and the plate ("on horseback" on both) very flexible peripheral seals (6) which will be compressed during loading under the effect of a jack (14) then kept compressed then under the effect of vacuum so that they marry  the groove profile of the cylinder as well as that of the two ends of the plate  so as to constitute inside the three elements (head flange, groove sectors  under the plate and tail flange) a sealed volume inside which we can make  the void.  3) Device according to claim 2 characterized in that the flanges (3) and (4)  will have at their ends a locking system (9) actuated during the cycles  loading and unloading by a micro jack (16) integral with the  handling of the flanges illustrated in figure 8 then kept locked by a powerful  leaf spring (11) during machine operation (cylinder rotation) to  act as safety in case of failure of the vacuum generator.  4) Device according to one of claims 1 to 3 characterized in that the two ends of the plate will be kept perfectly flat on the surface of the cylinder by a series of pads made of soft material (20) or any other system, integral with the flanges and capable of crash without affecting the proper functioning of the system.  5) Device according to any one of claims there 4 characterized in that the flanges (3) and (4), will be handled during the loading and unloading cycles by two stationary systems (Figure 8) which will allow them place and then deposit them by gripping with electromagnets (15) (or with suction cups) applied to metal plates (17) integral with the flanges and whose translational movement necessary for these operations will be obtained by one (or two) pneumatic cylinder (13) and whose guidance will be provided by two ball guide columns (14).  6) Device according to claim 5 characterized in that during each unloading cycle, at the time of gripping, the head flanges (3) and tail (4) will be perfectly repositioned by positioning feet (18) integral with handling systems shown diagrammatically in FIG. 8 which will be introduced into conical centering barrels (19) fixed on the flanges (3) and (4).