Web wrinkling resulting from moment transfer

Abstract

Considerable research has been focused on the impact of roller misalignment on web instability. Early work focused on the prediction of trough instabilities in the entering span, just upstream of the misaligned roller [1]. Later works involving misaligned [2] and tapered [3] rollers proved that the trough instability was a required precursor for the occurrence of wrinkles on the misaligned or tapered roller. The compressive stress required to induce web wrinkles on a roller can be 2 orders of magnitude larger, in the absolute sense, than the compressive stress required to precipitate trough instabilities in a web span. These works [2][3] found the out-of-plane web deformation due to troughs was responsible for creating the larger compressive stresses that would finally result in wrinkles whenever the misalignment or taper became sufficient. The three works referenced thus far all rely upon an assumption that the friction forces between the web and the upstream roller, which separates the entering and pre-entering spans, are sufficient to prevent moment transfer. The lateral deformation of the web in the pre-entering and entering spans as a result of moment transfer has been another focus of web handling research [4][5]. This publication will focus on the impact of moment transfer on web wrinkling. It will be shown that troughs may now occur in both the pre-entering and entering spans. It will also be shown that wrinkles can precipitate on either the misaligned roller or the roller upstream of the misaligned roller. It will be shown that these behaviors can be predicted and the predictions will be validated by test results. It will be shown that as a result of moment transfer the roller misalignment to induce wrinkles can be less than the misalignment required to induce wrinkles when moment transfer does not occur.