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Monday, May 11, 2015

Roll Hardness vs. Reel Weight and Moisture

Years ago Beloit produced a video illustrating that a properly wound and wrapped roll was stable for months, and potentially even years, when wrapped and protected from the environment. However, what happens when the moisture variation is inside the roll wrapper?



The environment inside the roll and the roll wrap come to equilibrium in just a few weeks or months. This means that with time, the wet streaks in a roll will lose moisture and the dry portions of the roll will pick up that moisture until the roll eventually reaches a uniform moisture or an equilibrium. As a dry streak picks up moisture in a roll achieving equilibrium, each sheet grows slightly with increasing moisture and the dry streak develops into a ridge. While the root cause may be identified as caliper variation, that variation may not exist as the roll comes off the machine winder. 

In the example above, it took nearly one month before the moisture variation in the base sheet showed up in the rolls waiting to be coated by our customer. Unfortunately, it took several months just to start looking at the paper machine and the coating base, and these defects and the costs associated with these claims amounted to over $400,000, before corrections were made and the mapping for weight, and moisture, variation was corrected. The eventual proof was found in coating base rolls that had been set aside or quarantined at the specialty coating plant and then returned to the paper mill for machine and winder operators to see and feel the severity of ridges in the coating base. Roll hardness profiles, such as those provided by a ACA Systems RoQ, were also proven as a tool for measuring roll quality defects such as the ridges that developed even in the uncoated base paper.

Visit the Technidyne Website for information on this and many other applications.