Lateral dynamics simulation of webs having cross-machine direction variation

Webs often include sectional variation in caliper or modulus of elasticity as a result of undesirable manufacturing variation or by intentional design. These variations influence wrinkle formation and tracking control in multi-span web handling systems. This paper shares the results of finite element simulations of the lateral dynamics of webs having variation in thickness and modulus in cross-machine direction. Span length and machine-direction bulk strain were varied and the effects on lateral steering and wrinkle formation were simulated for a variety of inhomogeneous webs.Key variables affecting the lateral steering include the CMD location of the thick section and its width, the stiffness of the thick section, the z-direction bias of the thick section relative to the roller surface, the average strain in the composite web and the span length/width ratio. The web shifted in most cases toward the half of the web having the thick section, though not all. The combination of a web with a thick, stiff section having a width 1/10-1/6 that of the base web, coincident with the web edge, in long spans with low strain generated the largest lateral shift. Wrinkles were generated for some conditions where the thick section was located on or near web centerline

Impacts of a 90 degree twist on lateral web dynamics

Twists are sometimes used to turn or provide passive lateral control for narrow webs in those cases where space for a sufficient twist span length (to avoid a wrinkle) is achievable. This paper uses the finite element method to study the lateral dynamics of a web downstream of a 90 degree twist in response to an upstream lateral disturbance. A designed experiment of 46 different finite element runs was used to study the interactions among different material, geometry, and input variables. Specifically, the frequency response for downstream cross-direction position was modeled as a function of the disturbance frequency, disturbance amplitude, span length, wrap angle and material stiffness. Nominal strain was held constant. A composite Gaussian process model was fit to the resulting data to facilitate a deeper and more holistic interpretation. Excellent attenuation of the disturbance amplitude and interesting interactions with the applied frequency and twist span length were shown

Wrinkling mechanisms of webs with spatially varying material properties

Webs often include variation in caliper or modulus of elasticity as a result of manufacturing variation. Light-weight nonwoven webs are especially prone to these issues because the variation is proportionally more, relative to the average modulus. It is proposed that the length scale variability in fiber orientation and most importantly mass density extends to the mechanical properties of the web, including the degree of orthotropy and Poisson's ratio (neckdown behavior). Finite element simulations show that materials exhibiting this kind of variability (in MD and CMD modulus, and Poisson's ratio), notably with nominally high and low regions alternating in the MD, leads to trough and wrinkle formation. Multiple simulations with varied material properties have led to a greater understanding of the mechanisms and conditions that cause these types of wrinkles