Understanding Rolling NIP Action Through Video Technology, 1993 Finishing and Converting Conference Proceedings

J. David Pfeiffer

Rolling nips in winding occur wherever a cylindrical winder drum or contacting roller bears against the winding product roll of web material. These nips are employed to exclude air in the winding, to produce a tight start in winding, to firm up an otherwise soft roll, or to compensate for variations in the sheet profile. Frequently, a large percentage of roll weight is carried on winder drums. Quality control efforts often focus on the damage done, or suspected to be done by rolling nips. This includes the formation of roping, corrugations, and crepe wrinkles. To study the mechanism by which some of the defects might be formed, an apparatus has been constructed for viewing the edge of web layers just below the surface as the rolling nip passes by. The web strips, 15 or more, are placed on the roll body, simulated by a large steel ring 0.56 m in diameter. The webs and roll body are stationary, while a 0.2 m diameter nip roller is arranged to bear with the appropriate nip force while passing by externally. A closed circuit television camera and microscope plus video cassette recorder are used to inspect the motions of various layers in the nip. Strain gage force transducers attached to the paper webs provide numerical values for web tensions on both the ingoing and the exiting side of the nip pressure impulse. The basic form of displacement occurring in the webs may be detected visually, while the measure of before and after web tensions confirms the existence of motion opposite to nip-induced tensile straining, otherwise known as “J-line” motion. The observed effects support the development of strains by rotation about an instant center.