GB2048833A

GB2048833A - A printing press for obverse and reverse printing

Info

Publication number: GB2048833A
Application number: GB8014511A
Authority: GB
Original assignee: Polygraph Leipzig Kombinat Veb
Current assignee: Polygraph Leipzig Kombinat Veb
Priority date: 1979-05-07
Filing date: 1980-05-01
Publication date: 1980-12-17
Also published as: DE3009783A1; DD142953A1; GB2048833B; DE3009783C2; CH645573A5

Abstract

A printing press for obverse and reverse printing, comprising a series of individual printing mechanisms, a transfer drum between each adjacent individual printing mechanism, each transfer drum comprising a sheet turning device which initiates the turning of a sheet in the region of the sheet rear edge then to transfer the sheet from the surface of an impression cylinder by a suction system to an oscillating gripper system. Until the sheet is transferred to the gripper system, a deflection angle forms between the suction system and the impression cylinder which can result in the sheet separating from the suction system. This is overcome by a suction system comprising a plurality of suckers, each sucker comprising a body with a flexible lip (19) which is capable of deformation so that the sucker conforms to the surface of the sheet (12). <IMAGE>

Description

SPECIFICATION A printing press for obverse and reverse printing This invention relates to a printing press for obverse and reverse printing.

In obverse and reverse printing presses, comprising an impression cylinder and a sheet turning device which initiates the turning of a sheet in the region of the rear edge of the sheet, the sheet is transferred from the closed surface of the impression cylinder by a sucker system and is transferred to an oscillating gripper system.

German (Dem. Rep.) Patent Specification No.

54703 describes a sucker system for taking over a sheet from an impression cylinder, the sucker being firmly mounted on an oscillating shaft which is moved along a circular path in the swinging-in phase relative to the movement of a sheet guide roll with the sheet held by the suckers at its rear edge. As a result, until the sheet is transferred to the gripper system, a deflection angle forms between the suction head of the suction system and the sheet released from the impression cylinder, which angle reduces the holding force of the suckers. Especially where stiff printed materials such as cardboard or the like are being processed, this deflection angle can result in the sheet coming away from the suckers.

This disadvantage becomes especially noticeable as the rotational speed of the printing press increases, since at higher speeds a higher holding force is necessary.

It has also proved to be a disadvantage that the suckers are not sufficiently flexible to adapt to the differing material thicknesses of the printed materials. When processing printed materials of a different thickness, therefore, the suckers must be changed when the printing press is reset, which consequently increases the resetting time.

The lack of flexibility of the suckers has also proved a drawback in that, when they come down on the rear edge of the sheet resting on the impression cylinder, shocks occur which cannot be accepted by the suckers and which are transmitted to the oscillating shafts, consequently these shocks have an adverse effect upon the necessary guidance of the sheet in respect of the lay mark and register.

The aim of this invention is to provide a printing press for obverse and reverse printing which avoids the need to change the suckers and which can be used for the processing of all thicknesses of material and which makes possible turning of the sheet with accurate register even at high rotational machine speeds.

According to the invention there is provided a printing press comprising at least two printing mechanisms each comprising an impression cylinder, and a respective transfer drum between successive ones of the printing mechanisms for turning a sheet starting from its trailing edge, each transfer drum being provided with a plurality of suckers and a gripper system, the suckers being co-operable with the gripper system to pick up a sheet from the impression cylinder and transfer it to the gripper system, and each sucker comprising a body with a flexible lip which is deformable to adapt to the surface of the sheet to be turned.

Preferably, the body of the sucker is furnished with a bore extending through the body to a suction surface, and the suction lip, in the region of the suction surface is formed with a suction channel which communicates with the bore.

To improve the accuracy of register of the sucker, a steel tube can be incorporated into the bore.

The suction lip may be disposed on either side on the suction body. Such a construction of the sucker offers the advantage that the elastic suction lip can adapt with its section surface to the stretched sheet becoming detached from the impression cylinder, so that the deflection angle between suction surface and sheet is to a great extent compensated. The sucker thus acts upon the sheet without reduction of the suction force, so that all types of printing materials that may be used can be handled even at high rotational speeds. The elasticity of the sucker offers the advantage that the sucker becomes seated softly upon the impression cylinder. Impacts and resultant vibrations, which can adversely influence the printed result, are thereby avoided.By such a form of construction of the sucker, it is no longer necessary to change the sucker when processing printed materials of differing thicknesses.

Because of its flexibility, the sucker is capable of adapting to the particular printed material thickness when processing anything from thin printing paper to cardboard, while the accuracy of register in turning the sheet is improved, avoiding complicated operations in the conversion of the printing press.

An embodiment of the invention will now be more particularly described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a partial elevation of a multi-colour sheet rotary printing press for obverse and reverse printing, Fig. 2 is a fragmentary detail of a sheet turning device in the phase of guiding the sheet through the suction system of the printing press, Fig. 3 is a cross-section through a sucker taken radially of the transfer drum, Fig. 4 is a plan view of the sucker shown in Fig.

3, Fig. 5 is a view similar to Fig. 3 showing the adapting of the sucker to the printed material, and Fig. 6 is a transverse section of another form of embodiment of the sucker.

Referring now to the drawings in detail a muiticolour sheet rotary printing press, which can be used either for obverse printing or for obverse and reverse printing, comprises a feed table 1, a first printing mechanism 2, including a preliminary gripper 3, a feed drum 4, an impression cylinder 5, a rubber roller 6, a plate roller 7 and a transfer drum, constructed as a turning drum 8, which connects together the first printing mechanisms 2 with a second printing mechanism located at the position 9.

The turning drum 8 is equipped,for obverse and reverse printing, with a suction system 10 and gripper system 11 operating in conjunction therewith. The drive for the suction and gripper system 10, 11 is provided by known means (not shown).

In Fig. 2 the turning drum 8 in its function for obverse and reverse printing, grips the sheet 12 by the suction system 10 at its rear edge and feeds it to the gripper system 11.

The suction system 10 is composed of a number of suckers 13, disposed across the width of the turning drum 8. Each sucker 13 (see Fig. 3) consists of a body 21 furnished with a bore 16 and a flexible lip 1 9. The sucker 1 3 is fixed to a suction bar 14, which is mounted in known manner on an oscillating shaft 1 5 (see Fig. 2). In the region of a suction surface 17, the body 21 and the flexible lip 1 9 of the sucker are traversed by a channel 18 which leads into the bore 16. A suction pipe (not shown) is connected with the bore 1 6 and to a vacuum generator (not shown).

According to another form of embodiment illustrated in Fig. 6, in order to improve the accuracy of register of the sucker 13, a steel tube 20 which does not extend quite as far as the region of the suction surface 17, is introduced into the bore 16. According to this embodiment, the flexible lip 1 9 is disposed on both sides of the body 21.

The method of operation of the rotary printing press is as follows: A sheet 12, oriented on the feed table 1 , is supplied by the preliminary gripper 3 and feed drum 4 to the printing roll 5. The sheet is printed on this roll in known manner and then, in the case of obverse and reverse printing, is gripped at its rear edge by the suction system 10 at the tangent point t,. t2 (see Fig. 1) of the impression cylinder 5 and the turning drum 8. The sheet is then passed over to the gripper system 11 and is fed by the latter to the second printing mechanism located at position 9.

A deflection angle a, (see Fig. 2) occurs during the rotation of the turning drum 8 between the suction surface 1 7 of the sucker 13 and the stretched sheet 12 becoming loosened from the impression cylinder 5. This angle which can only be compensated, to an insufficient extent, by the choice of the movement for the drive of the suction system 10, is assisted to the greatest possible extent by the flexible lip 19 (see Fig. 5). In the same manner and to the same extent, the flexible lip 1 9 assures a soft coming-to-rest upon the printing roll 5.

The suction device thus has the advantage that in sheet turning devices of obverse and reverse printing presses the deflection angle a which occurs between sheet and suction surface due to the swinging-in movement is as far as possible compensated by high flexibility of the sucker and moreover a soft coming-to-rest upon the impression cylinder is achieved.

Claims

1. A printing press comprising at least two printing mechanisms each comprising an impression cylinder, and a respective transfer drum between successive ones of the printing mechanisms for turning a sheet starting from its trailing edge, each transfer drum being provided with a plurality of suckers and a gripper system, the suckers being co-operable with the gripper system to pick up a sheet from the impression cylinder and transfer it to the gripper system, and each sucker comprising a body with a flexible lip which is deformable to adapt to the surface of the sheet to be turned.

2. A printing press as claimed in claim 1, wherein each sucker is formed with a bore extending through the body to a suction surface which is provided at least partly on the lip, the suction surface of the lip being provided with a channel communicating with the bore.

3. A printing press as claimed in either claim 1 or claim 2, comprising two such lips disposed one at each of two opposite sides of the body.

4. A printing press as claimed in either claim 2 or claim 3, wherein a tube is provided in the bore.

5. A printing press as claimed in claim 4, wherein the tube comprises steel.

6. A printing press substantially as hereinbefore described with reference to Figs. 1 to 5 of the accompanying drawings.

7. A printing press substantially as hereinbefore described with reference to Figs. 1 and 6 of the accompanying drawings.