Effects of Furnish-related Factors on Tension and Relaxation of Wet Webs

Abstract

A smooth web transfer in a paper machine requires sufficient tension. It is well known that excessive tension leads to web breaks. However, too low a tension can also be fatal. Particularly with wet web, the maintenance of the tension is challenging due to the fast relaxation of the tension. Some factors that affect the tension and relaxation of wet web were studied in this paper.

The initial tension and the tension after constant relaxation time, called residual tension, was found to depend on factors such as the applied strain, straining rate, dry solids content, fibre and fines properties, substances in the white water, and the dry strength chemicals. The residual tension was reduced by increased straining rate, addition of TMP filtrate, and addition of cationic starch. The tension and residual tension seemed to be dependent on both the properties of the fibre fraction, such as in- and out-of plane stiffness, and on the factors affecting the stress transfer conditions at the inter-fibre contact areas.