GB2092956A

GB2092956A - Plate cylinders for sheet-fed rotogravure printing presses

Info

Publication number: GB2092956A
Application number: GB8138514A
Authority: GB
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 1980-12-24
Filing date: 1981-12-22
Publication date: 1982-08-25
Also published as: FR2496557B1; JPS57128555A; CH653617A5; DE3049143A1; FR2496557A1

Abstract

A plate cylinder for a sheet-fed rotogravure printing press has means for securing a flexible printing plate thereon which are adapted to seal the cylinder gap as the plate is mounted and tensioned around the plate cylinder. The cylinder has a gap in which is set a locking device. The locking device base (2) has a semicircular bearing groove (3) extending over its length, in which a one-part clamp (4) pivots about an axis (12). The clamp (4) has a clamping surface (5) facing, at a defined spacing (A) a clamping surface (6) provided on the locking device base (2). The printing plate is mounted between both clamping surfaces (5 and 6) and secured by the swivelling movement of the locking device (2) about a shaft (8). The swivelling movement is actuated by means of a toggle drive (10, 11). <IMAGE>

Description

SPECIFICATION Plate cylinders for sheet-fed rotogravure printing presses This invention relates to plate cylinders for sheet-fed rotogravure printing presses. Such cylinders are known conventionally to include a cylinder gap, in which means for securing a flexible printing plate and sealing the cylinder gap are provided, one end of the printing plate being placed around the edge of the cylinder gap and the other end brought into contact with a locking device, the printing plate being tensioned by swivelling the locking device which is mounted on a rotatable shaft in the cylinder gap. The sealing of the cylinder gap is necessary since on rotogravure presses it is customary to feed the printing ink directly to the printing forme or plate and remove the excess quantity by a doctor blade.

Hence the aim is always to provide a printing forme which preferably has no joints but can be mounted easily and simply on the plate cylinder. A printing forme with a minimum of joints is desirable, because the doctor blade cannot be withdrawn periodically from the printing forme.

Arrangements which meet these requirements are already known from various patents and show possible ways of tensioning the printing formes or printing plates. U.S. Patent Specification 2 157 621 describes an arrangement in which the bent ends of the printing plate are inserted in a recess in a clamp and tensioned by swivelling the latter. Another method of tensioning plates is described in German Patent Specification 454951. In this refinement the ends of the printing plate are provided with detachable bars, which can be secured to the cylinder and a locking segment. However, these arrangements have disadvantages, so that they cannot be easily used for a sheet-fed rotogravure press.The arrangement according to German Patent Specification 454 951 should be regarded as particularly disadvantageous, because additional bars are required on the ends of the printing plates.

The particular disadvantage of the arrangement according to U.S. Patent Specification 2 157 621 is that a refinement of this type can be used only for cylinders with a narrow gap, because with a wider gap the printing plate would not be supported over a greater distance. In addition, the end of the printing plate moved during the tensioning operation is not adequately secured.

According to the present invention there is provided a plate cylinder for a sheet-fed rotogravure printing press, the cylinder including a cylinder gap, means for securing a flexible printing plate around the periphery of the cylinder and means for sealing the cylinder gap, the securing means including a locking device arranged on a rotatable shaft in the cylinder gap in such a way as to enable a printing plate to be placed with one end around an edge of the cylinder gap and the other end in contact with the locking device and to be tensioned by swivelling the locking device on the rotatable shaft, wherein the locking device comprises a base member mounted on the shaft and having a semi-circular bearing groove extending over its length, a one-part clamp member extending over the length of the bearing groove and pivoted in the latter, the base member and clamp member having facing clamping areas which can be brought to lie closer together than the thickness of a printing plate to be clamped, and a toggle drive connected to the base member, the swivelling movement of the locking device being actuated by the toggle drive to enable the locking device to be locked in position with a plate tensioned around the periphery of the cylinder. Such a plate cylinder can be used in a sheet-fed rotogravure press. The printing plate tensioning device arranged in the cylinder gap can be constructed simply and reliably, so that when operated it acts to seal the gap so that penetration of ink is reliably prevented, while at the same time properly clamping the printing plate when the gap is closed.

Compared with the known arrangements the arrangement according to the invention has important advantages. In particular, the locking device can be constructed so that it is inserted radially into the gap, so that only a small part of the plate cannot be supported at the cylinder circumference. The printing plate can also be clamped relatively easily, because this can be done automatically.

In a particular embodiment of the invention the construction is such as to enable one end of the printing plate to be pushed into a clamping bar provided for this purpose when printing starts and clamped by partially closing the gap. After a partial revolution of the gravure cylinder the other end of the printing plate can then be pushed into a clamp and clamped by further closing of the gap. At the same time the printing plate is tensioned by further closing of the locking device.

The invention is explained in more detail below with reference to the accompanying drawing which shows a section of an example of a gravure cylinder according to the invention.

Referring to the drawing, a plate cylinder 1 has a gap 9 extending over its length, in which means for clamping and tensioning a printing plate 7 are arranged. The clamping and tensioning devices are mounted rotatably on a shaft 8 in the gap 9 and can be fixed in their clamping and tensioning position by a toggle drive 10, 11. The clamping and tensioning devices can be inserted into the gap 9 by operating the toggle drive 10,11. When the clamping and tensioning devices are inserted into the gap 9, the printing plate 7 is detensioned and released. The clamping and tensioning devices are combined in one unit consisting of a locking device 2, which is mounted on the shaft 8 and can be operated by the toggle drive 10, 11.The locking device 2 has a semi-circular bearing groove 3, in which a clamp 4 is mounted with a suitably shaped lug 15. The locking device 2 and clamp 4 each have a clamping area 5 and 6, between which the printing plate 7 can be clamped. To achieve a higher holding force, the clamping areas 5 and 6 can have a roughened surface. The printing plate 7 is clamped and tensioned by bending the ends of the printing plate 7 and placing them around the edges 13, 14 of the plate cylinder 1 and clamp 4, one end of the printing plate being pushed between the clamping areas 5 and 6 of clamp 4 and locking device 2. The end of the printing plate 7 remaining at rest when the printing plate 7 is tensioned is adequately secured between the cylinder gap area 14a and a possibly flexible holder 16.The locking device 2 is lifted out of the gap 9 by actuating the toggle drive 10, 11 and moved in the direction of the edge 14 of the plate cylinder 1.

The two clamping areas 5 and 6 are pressed against each other by the resulting tension exerted by the printing plate 7 on the clamp 4, the printing plate 7 arranged between them being clamped. The printing plate 7 is then tensioned by further actuation of the locking device 2 in the direction of the edge 14, and the gap 9 is closed at the same time. The slot B at the joints at the ends of the printing plate can be sealed buy a plastics strip 17, which can be placed between the ends of the printing plate before the final closing of the gap 9.

The projecting plastics material should then be cut off with a knife, so that the upper surface of the plastics strip 17 is level with the surface of the printing plate 7. As it is customary to remove ink from the printing forme by a doctor blade in gravure printing, the edges 13 and 14 of the clamp 4 and plate cylinder 1 are slightly inclined to the plate cylinder axis, e.g. by about 45'. Consequently the doctor blade which can be placed against the plate cylinder 1, can be prevented from springing as the joint between the end of the printing plate passes beneath it and spraying of ink is thus avoided.

Claims

1. A plate cylinder for a sheet-fed rotogravure printing press, the cylinder including a cylinder gap, means for securing a flexible printing plate around the periphery of the cylinder and means for sealing the cylinder gap, the securing means including a locking device arranged on a rotatable shaft in the cylinder gap in such a way as to enable a printing plate to be placed with the end around an edge of the cylinder gap and the other end in contact with the locking device and to be tensioned by swivelling the locking device on the rotatable shaft, wherein the locking device comprises a base member mounted on the shaft and having a semi-circular bearing groove extending over its length, a one-part clamp member extending overthe length of the bearing groove and pivoted in the latter, the base member and clamp member having facing clamping areas which can be brought to lie closertogetherthan the thickness of a printing plate to be clamped, and a toggle drive connected to the base member, the swivelling movement of the locking device being actuated by the toggle drive to enable the locking device to be iocked in position with a plate tensioned around the periphery of the cylinder.

2. A plate cylinder according to claim 1, wherein the surface of the facing clamping areas are rough.

3. A plate cylinder according to claim 1, wherein, a printing plate is tensioned on the cylinder, the one-part clamp member rotates around the pivotal axis in the bearing groove to bring its facing clamping area towards the clamping area of the base member of the locking device.

4. A plate cylinder according to any one of claims 1 to 3 wherein the edges of the cylinder gap and of the clamp member are inclined at an angle of approximately 45' to the cylinder axis.

5. A plate cylinder for a printing press substantially as hereinbefore described with reference to the accompanying drawing.

6. An assembly of a plate cylinder according to any one of claims 1 to 5 and a plate, wherein the plate is tensioned about the cylinder and the slot between its ends still remaining after tensioning of the plate is sealed by a plastics strip.

7. A printing press including a plate cylinder according to any one of claims 1 to 5.