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Instrumenting rolling nips for video recording and strain recording

Pfeiffer, J. D.

An apparatus has been constructed to study the effect of a rolling nip on multiple layers of paper or other material. The use of a roller in contact with the surface of a winding product roll excludes air and produces higher levels of winding tension than when the web is brought into contact with the roll without nip contact. However, rolling nips are suspected of producing a number of side effects such as crepe wrinkles, torsional twisting within the roll body leading to roping and corrugations, and possible generation of bursts within the roll on weaker sheets. In this apparatus it is possible to measure the tension on each end of fifteen strips of material to study the effect of web tension and nip force on the residual tension distribution within the sheets. The roll body remains stationary while the nip travels around it, and this has allowed the installation of a continuous-focus microscope and closed circuit television camera to view the behavior of the webs as the nip passes by. Observation of differential motion between web layers is possible but difficult, as the total displacement is small. The strain gages have detected strain differences between the webs and results are reported for testing 15 webs of newsprint under different nip loading forces and web tensions.