Printing cylinder

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The printing cylinder is the part of the printing machine that functions as a pressure generating element. The pressure cylinder is often only referred to as a counter pressure . Printing cylinders are used in all high-speed presses, offset presses and also in extraction presses. The cylinder, like the platen in a platen press , carries the elevator . In almost all machine types , the pressure foundation is fixed and the pressure cylinder is adjustable to this.

construction

The pressure cylinder is preferably made of cast iron and is precision machined. With high-speed presses, it has a so-called recess for receiving the gripper bar and, depending on the design, is either round or cylindrical with a flattened part (e.g. two-speed machine). In the case of extraction presses without a system, the cylinder is often completely round without any indentation, since no elements for the printing material feed need to be arranged in the cylinder.

In simple machines, the cylinder is covered with a blanket or hard rubber and is often only pressed onto the substrate by its own weight. With high-speed and offset presses, the accuracy is approx. 1/100 mm and the cylinder is equipped with bearer rings . This ensures a constant circumference of a few 1/100 mm and a perfect register image.

Working principle

There are older designs in which the cylinder is guided over the fixed printing form. In most machines, however, the pressure foundation is passed under the permanently mounted cylinder and the cylinder is only raised or stopped as required. In rotary presses, the impression cylinder and forme cylinder are both fixed in their position.

General

Printing cylinders represent between 20 and 50% of the total machine weight. Cylinders that are too heavy are expensive. Cylinders that are too light, on the other hand, bend when printing heavy forms and produce an unclean print image. In particular, they cause uneconomical, lengthy set-up work. Badly balanced cylinders cause the machine to run unevenly and lead to rapid wear of the bearings. This is why the printing cylinder is still one of the most important elements of the printing machine today and, despite its simple appearance, is constantly being optimized in complex construction phases. In particular, the vibration mechanics with regard to torsional and bending vibrations is of particular interest and quality-determining.

Alternatives to the printing cylinder are the crucible ( crucible Druckmaschinen ) and the driver (driver presses for lithography ).

See also

The technical term cylinder is not to be confused with the popular name "cylinder" for entire letterpress printing machines in cylinder design. Typical of this is the name Original Heidelberger cylinder (OHZ) for a two-speed press from Heidelberger Druckmaschinen AG.