Part 3: Web Displacement Guide in Roll Coating Systems

In Part 2 of the Web Guiding Systems Series we discussed web steering guides.

Web Displacement Guide

Web Displacement Guide

Figure 3 – Web Displacement Guide

When a sufficiently long entry span is not available, a displacement guide may be a better choice. The displacement guide, as seen in Figure 3, is a system of four rollers. The first and last are fixed, while the center two rollers pivot on a common frame about the center of the upstream roller. The web sensor must be located very close to the exit of the third roller. While this is the most common depiction found in advertisements, the system can be arranged in at least 16 distinct ways, each of which have four orientations. These numerous equally effective possibilities allow considerable machine design flexibility.

The only real design constraints are that the spans entering and leaving the pivoting table must be at least 1/2 web widths long, but the three legs can be of different length. Note that the length between the pivoting rollers determines the effective sidelay range for a given twist of the web.

There is an important difference between the behavior of the displacement guide and the steering guide. While the steering guide will move the edge of the web upstream and consequently also downstream of the guide, the displacement guide will move only the downstream web path. Thus, the upstream process must be tolerant of uncontrolled web CD (cross direction) position.

In Part 4 of the Web Guiding Series we discuss Web Unwind and Rewind Guides.

Written for Faustel by David R. Roisum, Ph.D.