GB2258842A

GB2258842A - Apparatus for, and method of, mounting a printing plate on a cylinder of a printing press

Info

Publication number: GB2258842A
Application number: GB9118038A
Authority: GB
Inventors: Colin David Billows
Original assignee: BILLOWS Ltd
Current assignee: BILLOWS Ltd
Priority date: 1991-08-21
Filing date: 1991-08-21
Publication date: 1993-02-24
Also published as: GB9118038D0

Abstract

An arrangement for securing a (possible undersized) flexible printing plate to a printing cylinder comprises the provision on the cylinder of leading and trailing edge clamps which between them secure and tension a full sized cover sheet on the cylinder, one edge clamp being adapted to releasably receive an edge of the plate without consequential release of the underlying cover sheet. As described, the cover sheet is non-releasably secured to the leading edge clamp assembly (as by screws) and clamped by the trailing edge clamp, thereby leaving the clamp of the leading edge clamp assembly free for accepting the plate. The invention is adapted for the securement of undersized non-metallic (e.g. polyester) plates. <IMAGE>

Description

Apparatus for, and method of, clamping a printing plate to the cylinder of a printing press The present invention relates to an apparatus for, and a method of, clamping a printing plate to the cylinder of a printing press.

Traditional printing plates are made of metal, and are attached to the cylinder of a printing press by clamp bars which grip the leading and trailing edges of a plate so that it lies against the circumferential surface of the cylinder. One or both of the clamp bars are normally adjustable, allowing the printing plate to be placed in tension.

Recently, various kinds of non-metal printing plates have become available, which offer a number of advantages for certain types of work over traditional metal plates.

One such non-metal printing plate is that sold under the trade mark SILVER MASTER, which is made of polyester.

In order to reduce costs, polyester plates are often made to the size of the work to be produced, rather than the press size. Such a plate will extend only part of the way round the circumference of the cylinder, and so can be attached to the cylinder only at its leading edge, the trailing edge of the polyester plate being free. It is very important, therefore, that the method of attaching the plate to the cylinder is reliable and secure.

Packing material (consisting, for example, of plastics sheets) has to be provided between the printing plate and the cylinder. The packing material must be protected, and because part of the material will be exposed if the plate does not extend round the entire circumference of the cylinder, an aluminium cover plate is generally provided between the printing plate and the packing material. The cover plate is clamped at its leading and trailing edges and tensioned (in the same way as a traditional metal printing plate), and the leading edge of the polyester printing plate is clamped against the aluminium plate.

A disadvantage of this arrangement is that whenever the leading clamp bar is opened to allow the printing plate to be exchanged, the tension in the aluminium plate is released, and the plate must therefore be re-tensioned before resuming printing. This is time-consuming and inefficient, and can lead eventually to breakage of the aluminium plate. Further, the printing plate is not very securely held, and can easily slip or withdraw from the clamp while the cylinder is revolving or when the cover plate is tensioned.

According to the present invention, there is provided an apparatus for clamping a printing plate to a cylinder of a printing press, the apparatus including first and second clamp devices, a cover plate which, in use, extends around substantially the entire circumference of the cylinder and is secured at its leading and trailing edges to the first and second clamp devices respectively, and means for tensioning the cover plate, wherein the first clamp device is arranged to grip the leading edge of the printing plate, and is openable to release the printing plate without releasing the tension in the cover plate Because the printing plate can be removed without releasing the tension in the cover plate, the printing plate can be replaced very quickly and efficiently, thereby reducing the time that the printing press has to stand idle.The danger of the aluminium cover plate breaking is also significantly reduced, as re-tensioning of the plate is no longer necessary, Advantageously, the first clamp device includes upper and lower clamp jaws for gripping the leading edge of the printing plate, the leading edge of the cover plate being secured to the lower clamp jaw. Preferably, the leading edge of the cover plate is secured to the upper surface of the lower clamp jaw, the arrangement being such that when the printing plate is gripped by the first clamp device, the leading edge of the printing plate is located between the upper clamp jaw and the upper surface of the cover plate. The cover plate may be secured to the lower clamp jaw by fixing means which extend through holes in the leading edge of the cover plate into the lower clamp jaw.The clamping apparatus may be used for clamping a non-metal printing plate, for example a polyester printing plate to the cylinder of a printing press or, after removing the cover plate, for clamping a traditional metal printing plate to the cylinder. Removing the cover plate is relatively quick and easy, and the printing press may therefore be adapted readily from one type of plate to the other.

The first clamp device may include means for locating the printing plate in a predetermined position with respect to the cylinder. Advantageously, the locating means comprises two or more locating pins for engagement with apertures in the leading edge of the printing plate. Preferably, the locating pins are provided on the lower clamp jaw.

The present invention further provides a method of clamping a printing plate to a cylinder of a printing press, wherein the cylinder is covered by a cover plate which extends around substantially the entire circumference of the cylinder, the leading and trailing edges of the cover plate are secured to first and second clamp devices respectively and the cover plate is placed in tension, and the printing plate is gripped at its leading edge by the first clamp device, wherein the first clamp device can be opened to allow the printing plate to be removed or attached without releasing the tension in the cover plate.

The present invention yet further provides a printing press including a cylinder and an apparatus as described above for clamping a printing plate to the cylinder.

By way of example, an embodiment of the invention will now be described, with reference to the accompanying drawings, of which: Fig. 1 is a cross-sectional view of a cylinder of a printing press, having a printing plate attached thereto; Fig. 2 is a top view of a clamp bar; Fig. 3 is a rear view of the lower body member of the clamp bar; Fig. 4 is a cross-section through the clamp bar on line IV-IV of Fig. 2, and Fig. 5 is a cross-section through the lower body member of the clamp bar on line V-V of Fig. 2.

Figure 1 of the drawings shows, diagrammatically, the clamping apparatus of the present invention in use clamping a printing plate 1 to the cylinder 2 of a printing press. The printing plate may be manufactured from a non-metal material, for example polyester.

The cylinder 2 is of conventional design, and includes a recess 3 in which are located two clamp bars 4, 5. The cylinder 2 rotates, during operation, in the direction of the arrow A.

In order to protect the cylinder 2, it is covered by a plate 6, for example of aluminium, which extends around its circumference. The cover plate 6 is secured at its leading and trailing edges 7,8 by the clamp bars 5,4. A packing layer 9, for example of one or more plastics sheets, is provided between the cylinder 2 and the cover plate 6, to adjust the overall diameter of the covered cylinder to a predetermined size.

The printing plate 1, which might only extend part of the way round the circumference of the cylinder 2, is clamped at its leading edge 10 by the leading clamp bar 5, the trailing edge 11 of the plate being free.

The leading edge clamp bar 5, which is shown in more detail in figures 2 to 5, includes a lower body member 12 and a number of clamping members 13. The body member 12 is elongate and substantially uniform in transverse cross-section, comprising a rectangular base portion 14 having a raised rectangular lip 15 on its top face at the front edge thereof. The upper surface 16 of the lip forms the lower jaw of the clamp bar.

A plurality of screw holes 17 are provided in the lip 15, which holes extend perpendicularly to the upper surface 16 through the body member 14. The holes 17 are countersunk and tapped to receive screws 18. In one embodiment of the invention, the holes 17 are spaced 150mm apart, and the clamp bar 12 is approximately 1200mm long.

Two cylindrical bores 19 are provided in the lip 15, towards the ends of the body member 14. The bores 19 extend perpendicularly to the upper surface 16 through the body member 14, and receive pins 20 for accurately locating a printing plate with respect to the clamp bar 12. The pins 20 each have a cylindrical body and an enlarged head, and are secured in the bores by grub screws 21, located in tapped bores 22 that extend to the cylindrical bores 19 from the front face of the body member 14.

A groove 23 of semi-circular cross-section is provided in the top face of the base portion 14 towards its rear edge, in which there is seated a cylindrical rod 24 having a flattened face 25. The cylindrical rod 24 forms part of a quick release mechanism, which allows the clamp bar to be opened quickly, as will be described below.

The body member 14 is provided on its rear face and on its ends with screw adjuster devices 26, of known type, for adjusting the circumferential and transverse position of the clamp bar 12 relative to the cylinder 2.

The adjusters 26 are provided with graduations and cursors to allow their positions to be recorded.

In the embodiment shown in the drawings, four clamping members 13 are required, of which only two are shown. Each clamping member 13 is substantially rectangular in cross-section, and includes a forwardly-extending portion 27 and a rearwardly-extending portion 28.

The lower surface of the clamping member 13 is so shaped that when the clamping member 13 is seated on the lower body member 12 and the cylindrical rod 24 has its flattened face 25 uppermost, the rearwardly-extending portion 28, the central portion and the forwardlyextending portion 27 are in contact, respectively, with the flattened face 25 of the cylindrical rod, the top face of the base portion 14 and the upper surface 16 of the lip 15. The lower surface of the forwardly-extending portion 27 then forms the upper jaw of the clamp bar 5.

The upper front edge of the forwardly-extending portion 27 is chamfered, so that when the clamp bar 12 is located in the recess 3 of the cylinder 2, that edge does not project beyond the cylinder's surface. A number of semi-circular recesses 29 are provided in the front edge, to allow access to the locating pins 20 and the screws 18.

The clamping members 13 are secured to the body member 12 by bolts (not shown), which extend through bores 30 in the clamping members 13 and are received in tapped bores 31 in the body member 12. Springs (not shown), which are provided in the bores 30, lift the forwardly-extending portion 27 of the clamping member 13 when the cylindrical rod 24 has its flattened face uppermost, to allow a plate 1 to be removed or inserted into the clamp bar 5.

The trailing edge clamp bar 4 is similar to the leading clamp bar, except that screw holes are not provided in the raised lip 15 of the body member 12.

The cover plate 6 is provided in its leading edge 7 with a plurality of holes (not shown), which correspond in position to the screw holes 17 in the body member 12 of the leading clamp bar 5. The leading edge 7 of the cover plate 6 is secured to the body member 12 with screws 18 which pass through the holes in the cover plate 6 and are secured in the screw holes 17. As the screws 18 are tightened, the edges of the cover plate surrounding the holes are drawn into the countersunk upper portions of the screw holes 17, thereby forming a strong mechanical joint between the plate 6 and the body member 12 and allowing the heads of the screws 18 to lie flush with outer surface of the cover plate 6.

The trailing edge 8 of the cover plate 6 is secured to the trailing clamp bar 4 by clamping it between the upper and lower jaws of the clamp bar 4 and tightening the bolts, with the cylindrical bar 24 positioned so that its flat face 25 faces towards the rear of the clamp bar, so that the jaws grip the edge of the cover plate 6. The screw adjuster devices 26 on the rear faces of the body members 12 are then rotated to move the clamp bars 4,5 backwards (i.e. towards one another), thereby placing the cover plate 6 in tension.

The printing plate 1, which will already have had recesses or holes punched in its leading edge 10 at positions corresponding to the locating pins 20, is then located on the pins of the leading clamp bar 5, and the bolts are tightened, so that the edge of the printing plate is gripped between the upper clamp jaw and the upper surface of the cover plate 6. The printing plate 1 is thus attached very quickly, accurately and securely to the cylinder 2 of the printing press.

When it is necessary to fit a different printing plate to the cylinder 2, the cylindrical rod 24 of the leading clamp bar 5 is rotated until its flattened face 25 is uppermost, thereby opening the clamp bar 5 and allowing the printing plate 1 to be removed and replaced by the new one. The clamp bar 5 is closed again either by rotating the cylindrical rod 24 back to its previous position, or by re-tightening the bolts. Because the cover plate 6 is secured directly to the body member 12 of the leading clamp bar 5, the tension in the plate 6 is not lost when the clamp bar is opened. The printing plate 1 can therefore be replaced very quickly and easily, without the need to re-tension the cover plate 6.

Various modifications of the clamping system are possible. For example, the trailing clamp bar 4 may be identical to the leading clamp bar 5, being provided with screw holes 17 in its raised lip 15. The cover plate 6, which may have holes adjacent both its leading and trailing edges, can then be secured to both clamp bars 4,5 with screws, so that the tension in the cover plate is not lost even if both clamp bars are opened. Such an arrangement might be useful when using printing plates which extend all of the way round the circumference of the cylinder, and which have to be secured to the clamp bars at both edges.

Claims

1. An apparatus for clamping a printing plate to a cylinder of a printing press, the apparatus including first and second clamp devices, a cover plate which, in use, extends around substantially the entire circumference of the cylinder and is secured at its leading and trailing edges to the first and second clamp devices respectively, and means for tensioning the cover plate, wherein the first clamp device is arranged to grip the leading edge of the printing plate, and is openable to release the printing plate without releasing the tension in the cover plate.

2. An apparatus according to claim 1, in which the first clamp device includes upper and lower clamp jaws for gripping the leading edge of the printing plate, the leading edge of the cover plate being secured to the lower clamp jaw.

3. An apparatus according to claim 2, in which the leading edge of the cover plate is secured to the upper surface of the lower clamp jaw, the arrangement being such that when the printing plate is gripped by the first clamp device, the leading edge of the printing plate is located between the upper clamp jaw and the upper surface of the cover plate.

4. An apparatus according to claim 3, in which the cover plate is secured to the lower clamp jaw by fixing means which extend through holes in the leading edge of the cover plate into the lower clamp jaw.

5. An apparatus according to any one of the preceding claims, in which the first clamp device includes means for locating the printing plate in a predetermined position with respect to the cylinder.

6. An apparatus according to claim 5, in which the locating means comprises two or more locating pins for engagement with apertures in the leading edge of the printing plate.

7. An apparatus according to claim 6 when dependent on claim 2, in which the locating pins are provided on the lower clamp jaw.

8. An apparatus for clamping a printing plate to the cylinder of a printing press, the apparatus being substantially as described herein with reference to, and as illustrated by, the accompanying drawings.

9. A method of clamping a printing plate to a cylinder oaf a printing press, wherein the cylinder is covered by a cover plate which extends around substantially the entire circumference of the cylinder, the leading and trailing edges of the cover plate are secured to first and second clamp devices respectively and the cover plate is placed in tension, and the printing plate is gripped at its leading edge by the first clamp device, wherein the first clamp device can be opened to allow the printing plate to be removed or attached without releasing the tension in the cover plate.

10. The method of claim 9, in which the first clamp device includes upper and lower clamp jaws, and the leading edge of the cover plate is secured to the lower clamp jaw.

11. The method of claim 10, in which the leading edge of the cover plate is secured to the upper surface of the lower clamp jaw, and the leading edge of the printing plate is gripped between the upper clamp jaw and the upper surface of the cover plate.

12. The method of claim 11, in which the cover plate is secured to the lower clamp jaw by inserting fixing means through holes in the leading edge of the cover plate into the lower clamp jaw.

13. The method of any one of the claims 9 to 12, in which the printing plate is located in a predetermined position with respect to the cylinder by means of locating pins which engage apertures in the leading edge of the printing plate.

14. The method of claim 13 when dependent on claim 10, in which the locating pins are provided on the lower clamp jaw.

15. A method of clamping a printing plate to the cylinder of a printing press, the method being substantially as described herein with reference to, and as illustrated by, the accompanying drawings.

16. A printing press including a cylinder and an apparatus according to any one of claims 1 to 8 for clamping a printing plate to the cylinder.