Effect of air-side leakage in roll winding

Abstract

In web winding processes, a thin layer of air is entrained into rolls during winding. This air reduces the interlayer pressure in the wound roll because the air acts like a sponge between adjacent web layers. Winding models that include the effect of air entrainment have been developed in recent years to provide better prediction of wound-roll stresses and wound-roll quality. However, these models have limited predictive success in narrow-web winding, especially when a pressure roller is not used. During winding, and after a roll is wound, the air in the roll leaks out of the sidewalls through narrow gaps between the layers. The amount of air leaking through the sidewall, when the web is narrow and has a rough surface, is significant. When side leakage is not properly considered, the accuracy of the air entrainment model can be greatly affected. In this paper, a new winding model is developed that includes the effects of air entrained during winding and the subsequent air leakage through the sidewalls during and after winding. The formulation considers the effects of both pressure-roller and nonpressure-roller winding. Some results of this model are presented, together with comparisons to experimental results and predictions from other historical models (e.g., nonair entrainment and air entrainment without side leakage).