Do You Know What Causes the Variability in the Paper You Produce?, 2004 Paper Summit, Spring Technical & International Environmental Conference, (including Papermakers; Process Control, Electrical & Information; Product & Product Quality)

What is causing the MD streaks in your paper? Why can’t you get rid of calender barring? Why do you get uneven rolls from your winder? Do you have other chronic problems you just can’t seem to solve? Wouldn’t it be awful to replace your headbox and still have MD streaks because the problem is in your stock approach flow system? There is a way to answer these questions by testing the paper you produce.

We usually measure the paper we produce with on-line scanners and in the laboratory. Both of these measurements show us just a small amount of the variability in the paper. And, neither of these measurements is of much assistance in determining the cause of variability we might see.

On-line scanners mix MD and CD variability because they scan across a moving web. See Figure 1. A pulsation from a pump in the stock-approach flow system moves through the header from the inlet to recirculation. It will look like CD variation to the scanner system but is really MD variation. The software systems are designed to collect data for process control and some data analysis. They measure so many times per inch. See Figure 2. Their purpose is for process control. Conventional laboratory measurements, often used for quality control, are no more than spot checks, even when measurements are taken across the whole web.