Web tension and wrinkles in the printing press

Abstract

In a modem paper mill the web handling in every process stage is optimized to fulfill productivity demands. The same kind of demands also exist in the printing plants. Smooth production without runnability disturbances is a must in both cases. But in practise several problems still exist. Uneven paper profiles together with long web leads in 4-colour printing can be problematic. The shape of the web tension profile is often known but the variation across the web needs careful measurements. Because of differences in tension distribution, rolls cut from several positions on a paper machine reel can be totally different when printed in a 4-colour web.

Web tension measurements from paper machines to printing presses were carried out by the Graphic Arts Laboratory of the VTT. The same paper machine reel was measured with a portable set of measuring equipment both in a paper machine and in a winder. Laboratory analysis of the paper was carried out. The tension profiles of customer rolls were again measured in printing plants. The printed sheets were evaluated and the wrinkling phenomenon across the paper machine web was analysed. The results show that the profiles measured in printing presses originate from paper machines. Also the limitations of modem printing presses and paper itself must be taken into consideration when an optimum combination of tension and other paper profiles are aimed at in every process stage.