Analysis of web wrinkling in accumulators

Abstract

Accumulators provide a large amount of web storage in a small space. They are used to allow start/stop events like an unwind splice or a transfer to a new roll on a winder. It is common to see a loss of productivity due to wrinkles and lateral movement of the web as it travels through an accumulator.

An explicit finite element model has been developed to study wrinkle formation and web steering inside of an accumulator. Four cases will be presented: perfect web / perfect accumulator; imperfect web / perfect accumulator; perfect web / misaligned accumulator; imperfect web / misaligned accumulator. Model results indicate that the misalignment required to cause wrinkles within the accumulator decreases with increase in number of misaligned rollers. Model results also indicate that the critical misalignment to cause wrinkles decreases if the web has imperfections in the form of thickness variations.

A seven roller accumulator set up was designed and built to study the wrinkling dynamics of a low modulus nonwoven web and to compare the model results. Measurements indicate that the model predictions compare reasonably well to experiments. The study highlights the criticality of acceptable limits for tolerance on misalignments within the accumulator for process robustness.