Web troughs are deﬁned as an out-of-plane instability of a web in a free span between rollers. Troughs may be only an annoyance in some web process machines but are often detrimental to quality in coating or printing operations.
Web wrinkles are deﬁned as an out-of-plane instability of a web crossing a roller. Wrinkles are much more serious than troughs in that they result in creases, fold-overs, and bursts which can shut down a paper-making, coating, or printing operation or result in decreased quality or productivity.
This paper will provide proof that troughs are a necessary precursor to wrinkles. Examples will show that linear buckling analyses can be used to predict web troughs. Further examples will show how nonlinear post buckling analyses can then be used to predict wrinkling.