Grade Substitution Shipped under an Unchanged Product Name
Unannounced paper grade substitution alters structural fiber bonding and surface chemistry, demanding dockside physical and chemical testing before press loading.
Web Offset Press Tension
Web Tension
Pulling force applied to a continuous roll of paper as it travels through a printing press ensures the material remains flat and stable. Web offset press tension must be carefully balanced between the unwinder, the printing units and the folder to prevent the paper from wrinkling or snapping. It is controlled by a series of brake systems and driven rollers that react to changes in the press speed.
This parameter is the primary factor in maintaining accurate color registration over long distances.
Control Mechanism
Sensors known as load cells or dancer rollers monitor the tension in real time and send signals to the press computer. If the tension drops too low, the paper will sag and cause doubling or ghosting in the print image. Excessive tension stretches the paper beyond its elastic limit, leading to web breaks that require the press to be stopped and rethreaded.
The ideal setting depends on the basis weight and the moisture content of the stock. Thinner papers require a more delicate touch because they have a lower tensile strength and are more prone to tearing under load.
Production Stability
Maintaining a steady tension allows the press to run at its maximum rated speed without risking a catastrophic failure. It also ensures that the cut-off at the folder is consistent, which is necessary for the next stage of binding or finishing.