Growth and Decay of Straks and Waves on the Forming Table, 1997 Engineering Conference Proceedings

The surface waves and streaks on the forming table can cause problems in terms of nonuniform basis weight and moisture profile. In this study, we analyze the effects of viscosity and drainage on the decay of surface waves and streaks on the forming table. Large scale variations in physical properties which scale with the width of the paper machine are relatively well understood. In contrast, the cause of the small scale nonuniformities in the physical properties are not well understood. The length scales we refer to as small scale in this study are relative to the machine width and range from 0.02 to 0.5 m. Specifically, ultrasonic stiffness measurements of linerboard samples from commercial paper machines show small scale fluctuations in addition to the overall variations in the cross-machine direction (CD). Analysis of the paper machine show no physical features with the same length scale that could cause these nonuniformities except the wet streaks at the dry line on the forming table. We show the mechanism by which the streaks on the forming table evolve to form the characteristic nonuniformities in basis weight, moisture and stiffness properties.