Explicit analysis of the lateral mechanics of webs transiting concave rollers

Abstract

All previous analyses of webs encountering spreading devices have required enforcement of assumed boundary conditions. An example is the normal entry boundary condition which has been employed in many web/roller analyses. Explicit finite element analyses show much promise for studying all types of web handling problems. The primary benefit of this type of analysis is that only very basic assumptions are required, average web velocity and tension for example. Beyond this the interaction of webs with rollers are governed entirely by forces of contact and friction that develop between the web and rollers. Conditions of stick and slip are possible. Additional benefits include the ability to study web deformations and stresses which may reveal the boundary conditions that can be employed in models that are computationally less expensive.

This paper will focus on a study of the behavior of a web transiting a concave roller. It will be shown that a concave roller can be an effective spreader locally in the entry span as a web approaches a roller but can cause web instability in the form of troughs in an exit span. Results for several roller concavities, friction coefficients and web materials will be presented. Finally an assessment of when kinematic boundary conditions such as the normal entry condition are valid will be made.