A Winding Model for Unsteady Thermal Stress within Wound Roll Considering Entrained Air Effect on Heat Conduction

Abstract

Plastic film, formed as wound roll, is stored and transported under the various temperatures which can be different from the winding temperature. This temperature change affects the in-roll stress variation over time. As a result, it could lead to wound roll defect such as blocking or wrinkling. It is extremely important to theoretically estimate the in-roll stress in order to prevent the defect efficiently. In this study, a winding model for the unsteady thermal stress, considering entrained air effect on heat conduction in radial direction is presented. Air layer is formed between the wound films due to air entrainment during winding. On the winding model, the film is treated as equivalent layer combined with the air layer. In addition, the equivalent thermal conductivity, density and specific heat are taken into account the variation of contact between the wound films. Experimental verification result states that the predicted values correspond well to the experimental values. From a parametric study, it is shown that the air layer tends to influence on the heat conduction and the thermal stress if thermal conductivity of plastic film is high and the thickness of the air layer is thick.