GB2146949A

GB2146949A - Multi-impression printing machines

Info

Publication number: GB2146949A
Application number: GB08419410A
Authority: GB
Inventors: Peter Gertsch
Original assignee: Wifag Maschinenfabrik AG
Current assignee: Wifag Maschinenfabrik AG
Priority date: 1983-08-15
Filing date: 1984-07-30
Publication date: 1985-05-01
Also published as: CH665800A5; SE8304418L; SE8304418D0; SE455285B; GB8419410D0; DE3429079C2; DE3429079C3; FR2550730B1; FR2550730A1; GB2146949B; DE3429079A1

Abstract

In order to be able to counter web traction and lay mark problems occurring after the first drying and cooling operation, at least one of the impression cylinders 5, 10 is controllable with respect to peripheral speed independently of the plate-cylinder/rubber cylinder pairs 6, 11 associated therewith. This may be achieved by adjustable gearing, or the impression cylinder diameter may be varied, e.g. by controlled heating. <IMAGE>

Description

SPECIFICATION Rotary offset printing press The invention relates to rotary offset printing presses with printing units provided with impression cylinders, in which a print-carrying web is printed in at least two printing operations and after each printing operation is dried and is then cooled.

The change in the print length which occurs during the first drying and cooling operation represents a serious disadvantage in rotary offset printing presses of the above-mentioned type. The print length may, depending upon the quality of the web, undergo either extension or shrinking, and this can lead to considerable web traction and lay mark problems during the printing operation for the reverse side.

A rotary offset printing press is known from the German Offenlegungsschrift 31 31 170, in which the problem is solved in that the diameters of the printing unit cylinders are selected depending upon the nature of the paper, which is made possible by laying calibrated underlays beneath the rubber sheets or beneath the offset printing plates.

Such a procedure requires exact prior knowledge as to how the corresponding quality of the printcarrying web will react with respect to the print length in the first drying and cooling operation, and has the major disadvantage that the adaptation of the cylinder diameters can take place only when the machine is at a standstill and only before the insertion of the print-carrying web. It is not possible to react during operation to possible discrepancies in the assessment of the behaviour of the print-carrying web.

What is desired is a rotary offset printing press by means of which the web traction and lay mark problems can be countered during operation.

The present invention provides a rotary offset printing press with printing units provided with impression cylinders, in which a print-carrying web is printed in at least two printing operations and after each printing operation is dried and is then cooled, at least one impression cylinder being controllable with respect to peripheral speed independently of the pairs of plate cylinders and rubber cylinders associated therewith.

Two embodiments of the invention are described below, by way of example, with reference to the accompanying drawings, in which Figure 1 is a diagrammatic side view of a rotary offset printing press with two so-called satellite printing units; Figure 2 is a diagrammatic lateral view of a rotary offset printing press with a satellite printing unit for the two-stage passage of a half-width print-carrying web, and Figure 3 is a section through the impression cylinder of a satellite printing unit for a rotary offset printing press according to Figure 2.

In the rotary offset printing press illustrated diagrammatically in Figure 1 a print-carrying web 1 is drawn off in known manner from a storage roller 3 mounted in a roller changer 2 and is conveyed to a first satellite printing unit 4, where it is printed in four colours on one side by means of four pairs of plate cylinders and rubber cylinders 6 associated with a central impression cylinder 5. After this first printing operation the web 1 is dried in a first drier 7 and is subsequently conveyed by way of a first set of cooling rollers 8.

For the four-colour printing of the reverse the web 1 passes through a second satellite printing unit 9, which again comprises a central impression cylinder 10 with four plate-cyiinder/rubber-cylinder pairs 11 associated therewith. After the second printing operation the web 1 is dried again in a second drier 12 and subsequently conveyed to a folding apparatus 14 by way of a second set of cooling rollers 13.

Since the print length may vary according to the quality of the web 1 during the drying and cooling operation, sheet-traction and lay mark problems can arise for the second printing operation. In order to combat this during operation, at least one of the two impression cylinders 5, 10 is driven so as to be controllable with respect to peripheral speed and independently of the plate cylinder/rubber cylinder pairs 6, 11 associated therewith, for example by way of a fine-control gearing (not shown). The gearing control may be either manual or automatic in conjunction with known web-traction-measuring and register-sensing apparatus.

Peripheral speed may also be controlled by way of a change in the cylinder diameter. Since extremely small degrees of change are in fact involved, this may be attained in known manner by the effect of controllable thermal means.

It is also possible to put the invention into effect with a rotary offset printing press according to Figure 2. In this case too, the only half-width print-carrying web 15 is drawn off from a storage roller 16 and, as viewed in the axial direction, is conveyed to one half of a satellite printing unit 17. After the first printing operation it is dried in a drier 18 and is passed on to a turning apparatus 20 by way of a first set of cooling rollers 19. Here it is handled in known manner and is deflected sideways by at least its width parallel to its direction of travel. In order to print the reverse it now traverses the other half of the satellite printing unit 17. It is now dried again in the drier 18 and is conveyed to the folding apparatus 22 by way of a second set of cooling rollers 21.

In the case of this modification of the machine, the composite impression cylinder assembly 23 is subdivided into two cylinder halves 24, 25 (Figure 3) which can be driven independently of one another. The first cylinder half 24 is firmly secured to the cylinder shaft 26. The second cylinder half 25 is mounted freely rotatably on the cylinder shaft 26 and is firmly secured to a driving wheel 27, which is in engagement with a reduction gear 28. A controllable fine-control gearing, described with reference to Figure 1, is disposed in the drive connection for at least one of the two cylinder halves 24, 25.

Claims

1. A rotary offset printing press in which a print-carrying web is printed in at least two printing operations each followed by drying and cooling, the printing press including impression cylinders and associated plate-cylinder/rubber- cylinder pairs, at least one of the impression cylinders being provided with means for controlling its peripheral speed independently of the associated plate-cylinder/rubber-cylinder pair(s).

2. A printing press as claimed in claim 1, in which the peripheral speed controlling means comprises a fine-control gearing.

3. A printing press as claimed in claim 1, in which the diameter of the controllable impression cylinder is variable, the peripheral speed controlling means comprising means for controlling the diameter.

4. A printing press as claimed in claim 3, in which the said means comprise controllable thermal means.

5. A printing press as claimed in any preceding claim, in which the control of the peripheral velocity is automatic.

6. A printing press as claimed in any preceding claim, in which, for the two-stage passage of a half-width print-carrying web through a single printing unit, a composite impression cylinder assembly is divided into two halves drivable independently of one another, the two halves constituting the impression cylinders.

7. A rotary offset printing press substantially as described with reference to Figure 1 or Figures 2 and 3 of the accompanying drawings.