Feeding in rolling contact of layered printing cylinders

Many web handling processes involve nips through which the web passes. Due to contact deformations, the speed at which the nip cylinders feed the web may differ from the peripheral speed of the cylinders. This paper examines in detail the feeding phenomenon in the case of layered cylinders. In particular, we focus on offset printing cylinders which are covered by a thin rubbery layer. We begin our analysis by considering existing limiting solutions of thin layered cylinders undergoing small strains, and thereafter study the large deformation rolling contact problem using the finite element method. It turns out that the feeding tendency of layered cylinders is dominated by the compressibility of the layer. However, feeding characteristics of layered cylinders are not constant but rather depend on the applied indentation: an increase in indentation may even alter the feeding tendency of the cylinders. The results also indicate that the feeding type affects web strain. Consequently, we conclude that in order to attain better web handling, the feeding characteristics of the cylinders should be known.