Transport Elements of the Web Press

Web transport through the web press begins with the reel of paper or any other substrate on a reel; this is clamped in reel arms. To avoid production stoppages, the reels are almost exclusively changed in a fully-automated process by splicers.A separate infeed unit, also called pre-tensioning unit, is located after the reel stand for keeping web tension constant.

The printing unit itself serves also as a transporting element, because the web is transported under pressure between two cylinders. In the blanket-to-blanket unit of a web offset press these are two blanket cylinders (blanket-to-blanket mode), in gravure or flexographic printing (letterpress) they are a cylinder with a soft covering and a steel cylinder. Multicolor prints are produced by printing units arranged one after the other, which print the color separations onto the web. The web behavior during transport varies according to the cylinder surfaces, which requires a special dimensioning of the diameter of the steel cylinder and/or adaptations of the blanket cylinder packing.

Various finishing equipment is connected to the printing unit, such as the numbering unit, gluing station (for partial coating), dryers, chill roll assembly, slitters, turner bars, and perforators, as well as the formers and the folding unit, which all have some effect on web travel. To compensate for this the web travel is stabilized by driven draw rollers. In many applications (e.g., newspapers, magazines, catalogs) the folder with its cylinder section acts as a tensioning mechanism at the start of the web. Draw rollers acting on both sides are fitted at the entry of the folder, but it is the tucker blade cylinder of the jaw folder that exerts the actual tension. It is equipped with height-adjustable, curved plates or with circular shaped segments that correspond to the cylinder radius. The press does not need to be stopped for readjusting the tension, as it is equipped with a mechanism that allows adjustment during paper run. After the web or the ribbon bundle has been cross-cut in the folder, the

sheets are transported and delivered by means of pins or grippers in the cylinder section of the folder. The web can also be cut into individual sheets after printing using “sheeters”, and then stacked in a delivery like with sheet-fed presses.