ARRANGEMENT FOR AN ADJUSTABLE SHEET TURNING EQUIPMENT

Abstract: The invention refers to an arrangement for an adjustable sheet turning equipment in a sheet offset press of unit type for the printing of both sides of a sheet (1) and which includes only one transfer cylinder (2) between the printing units (3) in the press. The sheet (1) is held in a completely stretched condition on the transfer cylinder (1) before the turning regardless of the sheet size over a distance of the top half segment of the transfer cylinder (2) at least equalizing the length of the sheet to be turned and the turning of the sheet (1) is made between the giving transfer cylinder (2) and the receiving impression cylinder (8) in the following printing unit (3).

Description: Arrangement for an adjustable sheet turning equipment. The present invention refers to an arrangement for an ad¬ justable sheet turning equipment in a sheet offset press of unit type for the printing of both sides of a sheet and where said turning equipment includes only one transfer cylinder between the printing units in the sheet offset press. In sheet offset presses generally only one side of the sheet is printed at a time in a printing process. In single colour presses this is done in one printing unit, in two- or multi¬ colour presses in two or more printing units coupled together over one or three transfer cylinders for the transport of the sheet from one unit to the next, so called unit presses. Moreover, there are so called five cylinder presses, where two printing units are working against a common impression cylinder and where the transport of the sheet to the fol- lowing double printing unit is made with gripper bars carried on chains when multicolour printing. In unit presses as mentioned above there is a desire to re¬ duce the number of transfer cylinders between the units from three to one, as each gripper transfer which is required between the transfer cylinders among other things p.lso gives an extra risk for disturbances in the printing quality and also often higher manufacturing costs. Generally, both sides of the sheet should however be printed and in order to save the turning of the pile of paper and a renewal printing of the other side of the sheet, there are today adjustable presses which either print two or more colours on one side of the sheet or after adjustment print one or more colours also on the other side of the sheet at only one run through the press. In a two colour sheet offset press it is then possible to either print two colours on one side of the sheet or after adjustment one colour on each side of the sheet* Consequently, in a four colour sheet offset press either four colours can be printed on one side of the sheet or, after adjustment, two colours on each side and so on. At the adjustment the turning equipment is engaged. In unit presses Λis is installed in or operates against one or more of the transfer cylinders. In a five cylinder press the turning equipment is installed in an extra cylinder before the entrance to the receiving five cylinder unit. In the turning equipment the gripping of the sheet is changed from the fore edge to the rear edge and the sheet is then trans¬ ported with the original rear edge first and thus turned upside down and will in this way be printed in the following unit on the original back side of the sheet. The sheet is now printed on both sides at only one run through the press and without extra paper handling. The mechanisms which are re¬ quired in a .sheet offset press to make it adjustable as mentioned above are however rather complicated and then also expensive to make, they require more maintenance and can also influence the printing quality in negative direction. Particularly, it is required in today's technical solutions of this problem either to use three transfer cylinders between the printing units or sometimes also an extra cyl¬ inder outside the usual cylinder to turn the sheet. The more cylinders the more gripper transfers for the transport of the sheet and the greater the risk for disturbances in the printing quality, the more maintenance and the higher costs for the manufacture of the press. Multicolour presses of unit type and with only one transfer cylinder between the units are available, but with the giving cylinder as impression cylinder in the first unit and with the receiving and turning cylinder as transfer cylinder between the units. This means that either the stretching of the sheet which is required between the fore and the rear edge of the sheet in order to get an acceptable printing quality is not possible to install in the press, if the press is to be used for various paper sizes or that the giving impression cylinder will be extremely complicated in its 5 design. The object of the present invention is now to make an arrangement with an adjustable turning equipment in a street offset press as mentioned in the introduction by which the disadvantages in the mentioned designs are eliminated. The o essential and most important features area stated in the following claims. By means of the present invention a design has been made with an adjustable turning equipment in a sheet offset press of unit type which is made in such a way that only one transfer 5 cylinder between the printing units is -required and said transfer cylinder can hold the sheet stretched from its fore to its rear edge before the turning contrary to known designs which either require three ordinary transfer cylinders or one extra, only intended for this function, or with one transfer 0 cylinder only a very complicated impression cylinder in the first unit or a design which does not have the possibility to stretch the sheet on the giving cylinder. This is achieved according to the invention as the turning of the sheet, contrary to known solutions, is made between the giving 5 transfer cylinder and the receiving impression cylinder in the following printing unit. In the transfer cylinder the necessary stretching between the fore and the rear edges of the sheet is installed and this is so made that it can be adjusted for all paper sizes within the specification of the 0 press. The invention will now be more closely described below with reference to the enclosed drawings, of which Fig. 1 shows a schematic side view of a preferred design of an adjustable turning equipment according to the invention including a swing gripper which is located above the transfer point in a sheet offset press, Fig. 2 shows a schematic side view of a turning equipment according to another design within the present in¬ vention including a tumbling gripper arrangement in the impression cylinder in the following printing unit, and Fig. 3 shows a schematic side view of a third design of a turning equipment according to the present invention including a shifting gripper arrangement in the impression cylinder in the following printing unit. As can be seen from Fig. 1 a schematic side wiew of an ad- justable turning equipment in a sheet offset press of unit type is shown for the printing of both sides of sheet 1. This sheet offset press has only one transfer cylinder 2 which is installed between the two after each other following printing units 3. On the transfer cylinder 2 the sheet 1 is held in a completely stretched condition between the grippers 4 for the firm holding of the fore edge 6 of the sheet 1 and the suc¬ tion bar 5 for the location of the rear edge 7 of the sheet 1. The suction bar 5 should work with vacuum which through hoses and holes in the transfer cylinder, not shown on the , drawing, is maintained from a vacuum source. In the transfer cylinder 2 the mentioned necessary stretching of the sheet 1 between its fore edge 6 and rear edge 7 is made by making the suction bar 5 movable and this stretching is so designed that it can be adjusted for all desired sheet sizes within the press specification. The turning of the sheet is made between the giving transfer cylinder 2 and the receiving impression cylinder 8 in the following printing unit 3 over a distance of the surface of the transfer cylinder 2 on its top half segment. The turning equipment according to the example il¬ lustrated in Fig. 1 includes the swing gripper 11 which is located above the transfer point 12 between the transfer cylinder 2 and the receiving impression cylinder 8. As can be seen in Fig. 2 another design of a turning equip¬ ment is shown according to the present invention including a tumbling gripper arrangement 13 installed in the receiving impression cylinder 8. The purpose of this gripper arrange¬ ment is that it shall grip the rear edge 7 of the sheet 1 for turning the sheet 1 in the very transfer point 12 between the giving transfer cylinder 2 and the receiving impression cylinder 8. As can be seen in Fig. 3 a third design of a turning equip¬ ment is shown according to the present invention including a shifting gripper arrangement 14 installed in the receiving impression cylinder 8. The purpose of this gripper arrange¬ ment is that it shall grip the rear edge 7 of the sheet 1 for turning the sheet 1 in the very transfer point 12 between the giving transfer cylinder 2 and the receiving impression cylinder 8.

Claims: Claims 1. Arrangement for an adjustable sheet turning equipment in a street offset press of unit type for the printing of both sides of the streets (1) and where the turning equipment includes only one transfer cylinder (2) betweeen the after each other following printing units (3) in the sheet offset press, characterized in that the sheet (1) is arranged to be held in a completely stretched condition in a way known per se on the transfer cylinder (1) before the turning regardless of the sheet size over a distance of the top half segment of the transfer cylinder (2) at least equalizing the length of the sheet (1) to be turned and that the sheet turning is made between the giving transfer cylinder (2) and the receiving impression cylinder (8) in the following printing unit (3) . 2.. Arrangement according to claim 1, characterized in that the turning equipment includes swing gripper (11) which is located above the transfer point (12) between the transfer cylinder (2) and the receiving impression cylinder (8). 3. Arrangement according to claim 1, characterized in that the turning equipment includes tumbling (13) or shifting (14) gripper arrangements in the receiving impression cylinder (8), which are turning the sheet in the very transfer point (12) between the transfer cylinder (2) and the receiving impression cylinder (8) gripping the rear edge (7) of the sheet (1) before the turning of the sheet (1).

Inventors: ERIKSSON INGEMAR, ERIKSSON, INGEMAR
Applicants: SOLNA OFFSET AB
Application year: 1990
Main classification: B41F21
IPC codes: B41F21, B65H15