For convenience, webs are stored in wound rolls. The available web length in a wound roll is one mark of roll quality and a concern for many who process and convert webs. Elastic winding models have proven very precise at estimating the number of layers, the web length wound into a roll, and the residual stresses in the roll at the time of winding. Wound rolls can spend long periods of time in storage, where controlling the environment is cost-prohibitive. As many webs are viscoelastic on some time scale, the residual stresses due to winding will result in creep during storage. The changes in web length due to creep result in web process errors and quality loss, including registration errors and camber webs for example. This publication will focus on the development of a viscoelastic winding model to predict these changes in web length due to creep in a wound roll. The viscoelastic model predicts the tangential stress relaxation and radial creep due to winding residual stresses from a fully viscoelastic orthotropic material behavior. A spunned-meltblown-spunned (SMS) web and a low-density polyethylene (LDPE) web are taken as examples of viscoelastic webs. Their viscoelastic properties are systematically characterized using creep experiments. The results of the model show good agreement with winding and storage experiments for both webs. Finally, webs often do not creep uniformly across their width. An example of this non-uniform creep will be explored.
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Viscoelastic Web Curl due to Storage in Wound Rolls
While bending strains result from any web being wound at a radius of curvature into a roll, these bending strains are largest for the thicker homogeneous webs and laminates. Many webs are viscoelastic on some time scale and bending stresses will lead to creep. When the web material is unwound and cut into discrete samples, a residual curvature will remain. This curvature, called curl, is the inability for the web to lie flat at no tension. Curl is an undesirable web defect that causes loss of productivity in a subsequent web process. The goal of this research is to develop numerical and experimental tools by which process engineers can explore and mitigate machine direction curl in homogenous webs. Two numerical methods that allow the prediction of curl in a web are developed, a winding software based on bending recovery theory and the implementation of dynamic simulations of winding. One experimental method directly measures the curl online by taking advantage of the anticlastic bending resulting from the curl. All methods applied to a common isotropic LDPE web correlate well with each other and present an opportunity for process engineers to mitigate curl and its negative consequences at low time cost.
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- Award ID(s):
- 1635636
- NSF-PAR ID:
- 10110753
- Date Published:
- Journal Name:
- Proceedings of the Fifteenth International Conference on Web Handling
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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