Analysis of Moment Transfer in Multi-Span Web Systems

Abstract

Webs pass over numerous rollers in web processing machinery. A common problem is the formation of troughs and wrinkles in webs. Any out-of-plane web deformation in a span is called a trough and if this trough passes over a roller it may form a wrinkle. A major reason for the formation of troughs and wrinkles is the misalignment of the downstream roller in a span. As a result of misalignment moments are developed in the span upstream of the misaligned roller. The moment must be reacted by the frictional forces between the web and the upstream roller, where the moment is largest. If these frictional forces are not adequate a portion of the moment will be passed into the next span upstream. The focus of this research is to study moment transfers from one span to an upstream span and study the moments on the contact patch on the intermediate roller for the first time. An experimental setup was built to quantify amount of moments transferred for various amounts of misalignments. A finite element model was also developed to verify the experimental results. Laser Doppler Velocimeters (LDVs) were used to study the span interaction in web systems due to a misaligned downstream roller. The LDV is an industrial instrument capable of measuring the length of the material moving beneath them. The LDV's capability to measure length was used to calculate relative strain in a web span which can be related to moment. Moment measurements were made in entering span, pre-entering span, and on the roller dividing those two spans. Moments calculated from the experiments were verified by a newly developed FE model. The FE model estimated the amount of slippage associated with each level of misalignment and it proved to be a good predictor of the nature of web/roller interactions resulting due to a downstream misaligned roller.