Method for measuring wound-on-tension

Abstract

The Wound On Tension (WOT) is the web machine direction stress as it has just passed the winding nip into the roll. It is the most important quantity that determines the wound roll structure and its internal radial stress distribution. All the other winding parameters can affect the WOT but they can change the internal roll stresses only through the WOT. The on-line measurement of the WOT has been possible only in laboratory winders. However, if the WOT would be known, the winding parameters could be more accurately adjusted to give optimized customer roll structure. The purpose of this work has been to find and evaluate WOT measurement method feasible in the production environment. Both the usual Small deformations model known as the Hakiel model and the more recent Large deformations model were evaluated. The WOT can be solved from the Hakiel model numerical approximation and the measured radial displacement The numerical approximation is a large linear equation which can be reduced to a scalar equation linear for the WOT. The method is computationally effective allowing real time measurement of WOT during winding. The Density measurement is based on the roll length and diameter measurements giving the paper thickness and density when the basis weight is given. The web thickness under zero stress is needed to accurately measure the total radial displacement from this data. The results obtained with newsprint paper show that with paper grades having relatively low radial modulus the WOT can be measured at a reasonable accuracy if the free web paper thickness can be obtained from the preceding process machines.