Web break

In printing machines , preferably in web printing , or in machine paper production, a web break is understood to mean the unwanted separation of the paper web transversely to the machine direction.

If this occurs, the printing press must be stopped immediately, since the incoming end of the web tends to be wound onto various rollers of the printing units by an adhesive effect. This can lead to various types of machine damage, from the destruction of the printing form to bearing damage and even machine breakdown.

Web break control

In order to rule out this damage, today's machines are usually equipped with an optical web break control ( light barrier ) between each printing unit. After the infeed unit and after the last printing unit, so-called catch rollers are also used, which in the event of a web break, wind up the paper web and pull it out of the printing units. This process is very fast at machine speeds of up to 60,000 ex / h.

Web tension

The cause of the web break is often insufficient web tension, which leads to web flutter. The main cause of web tension problems is the dampening solution (alcohol / water mixture in offset machines ) or the printing ink (primarily gravure printing machines ), which lead to the swelling of the paper and thus web elongation. In the case of films, it is mainly a relaxation effect that leads to a decrease in web tension. Errors in the paper are also often a cause of the first scribe. Electrostatic charging effects also occur on very high-speed web presses and when the air humidity is too low , which promote "sticking" of the web and thus the tendency to tear.

Substrate roll

Other possible causes of web breaks can be paper defects, i.e. lateral damage to the roll, damage to the roll due to foreign objects (e.g. a nail or a screw that the roll rolled over during shipping or in the warehouse) or machine glue that occurs in paper production . Web breaks can also occur after the roll change. This can have different causes: Insufficient or too high dancer tension or negligent gluing on the new roll. In addition, many web breaks occur due to different moisture levels in the paper web. A roll that comes from the middle of a paper web during production has a completely different stretch behavior than an "edge roll". When printing these rolls, you should make sure that they are sorted accordingly. This measure makes work easier for printers and generally avoids unnecessary waste that otherwise occurs after every roll change.

Paper manufacturing

The web break or web break also occurs during paper production in the paper machine. There, in general, too high a web tension (e.g. due to missing or insufficient synchronization compensation during web drying) is the cause of the tear.