Dynamic Measurements of Stratified Consolidation in a Press NIP, 1992 Engineering Conference Proceedings

In situ measurements of stratified consolidation in a wet press nip are reported. New techniques were developed or forming handsheets with embedded targets at specified basis weight increments in the sheet. The measurements were made possible by improved techniques based on eddy-current transducers detecting the distance from thin copper-mesh targets embedded in a sheet. With these techniques, the thickness of several zones in a sheet could be tracked instantaneously during a pressing event.

The data show the dynamic development of higher density zones near the flow- exiting side of the sheet. Stratification of the sheet is well established by midnip and does not change substantially upon exiting the nip. Measurements were obtained in a variety of sheets, including hardwood and softwoods. Based on the available data, we found few significant differences in dynamic densification behavior between different furnishes. The results can be compared to other experimental results showing stratification after pressing.

Because the data also show the compression and expansion of various zones during the entire interval from .before nip closure to after nip expansion, information related to rewet is available. We examine the dynamic thickness of the flow-exiting side of the sheet and discuss the physics of rewet during nip expansion.