Wet End Survey - Measure and Source Basis Weight Variations (above 1 HZ)

Have you ever looked up through your paper at a source of light and seen large scale light and dark bands, particularly as the paper was traveling through the winder at low speed? Or has a paper analysis determined that there is excessive variability in your paper? In either of these cases, a wet end survey is recommended.

Basis weight in the sheet is determined by the mass of pulp fibers being frozen into the sheet. The uniformity of the basis weight depends upon the stability of the flow coming from the headbox, the stability of the headbox itself, the uniformity of the consistency of the stock, and the type of former.

In a typical wet end survey the basis weight variations from the Beta gauge are measured to determine the problem frequency.  Pressure pulsation measurements are taken on the taper header and upstream to the fan pump. Vibration measurements are taken on the headbox. The vibration measurements are extended to other components as necessary. Rotational speeds of the wet end components are determined and compared to the frequencies found in the basis weight.

If the variation is occurring at frequencies below 1 Hz, then a wet end audit is recommended. All this work needs an intimate knowledge of the process along with the dynamic characteristics of the equipment.