Corrugation and Buckling Defects in Wound Rolls

Sheet metal, paper, and polymer webs are often stored and processed as large rolls comprising thousands of layers. Depending on the elastic properties of the web material, the roll’s dimensions, the type of core, and the winding tension, the stresses that develop within the roll can be sufficiently high to cause local or gross buckling defects to form. For instance, the cylindrical core onto which the web is wound can collapse, a failure mode that is termed “v-buckling.” In other cases, while the core might remain intact, a group of layers interior to the roll can wrinkle into a near-sinusoidal corrugated pattern around the circumference. This paper examines such “starring” defects analytically and experimentally. Measurements on a laboratory-scale web transport system are used to validate the model, and to identify conditions where no defects occur and the roll has acceptable quality, where starring patterns develop, and where v-buckling occurs. For particular core and web materials, the tension and diameter are the primary variables that influence the roll’s stability, and demarcations between stable and buckled configurations are identified in the tension-diameter design space. A model for the elastic stability of the roll-core system is developed, in which the corrugated layers are treated as multiple rings subjected to the resultant pressure generated by the roll’s internal stresses, and to the elastic support provided by the core and neighboring web layers. At the onset of corrugation, adjacent web layers couple through surface contact which is incorporated in the model as an elastic shear layer.