Differentially driven S-wrap rolls for improved tension isolation

Abstract

Achieving adequate tension isolation is necessary in both the manufacture and subsequent processing of webs of all types. Several techniques currently are available including nips, vacuum rolls, driven rolls and S-wraps. From a combination of low cost and simplicity, S-wraps are the attractive alternative. They also are the best choice if the web is susceptible to surface damage. However, current S-wraps have deficiencies which are related to (1) torque loadings on the roll pair, and (2) problems controlling the web tension between the two rolls. These deficiencies can make it difficult to achieve good tension isolation. The differentially driven S-wrap system described here eliminates these problems and offers additional benefits. It provides a means to control the torque split between the driven rolls. This split makes it possible to shift the torque to the high tension side of the S-wrap where the available friction forces are higher. It also fixes the tension between the driven rolls without additional equipment. Finally, the differential action allows the rolls to operate at different speeds to adjust for differences in the roll diameters or web elongation.