The development of Wound-On-Tension in webs wound into rolls .

摘要

Scope and method of study. The Wound-on-Tension (WOT) is the tension in the outermost layer of a winding roll. The WOT controls the stresses in the wound roll and hence, the defects that can arise due to these stresses. Typically, rolls are wound with impinged nip rollers that exude air that might otherwise get entrained in the rolls. The nip rollers introduce tension in the web that is beyond the web line tension. Depending on the type of winding process, the WOT may have two components: one due to the nip roller and the other due to the web tension. In this thesis, the analysis of how the WOT is developed has been carried out. A first of a kind approach using the principles of contact mechanics and using a finite element tool has been attempted to model the nip mechanics. The surface tractions in the contact zone and the resulting slip and stick have been studied and their effect on the WOT is addressed.;Finding and conclusions. The numerical model shows that three distinct regions of contact exist in the top surface of the outer layer. At the edges of the contact zone, the top surface is under slip and travels faster than the nip roller. In the middle of the contact zone, the top surface is under stick and moves at the same velocity as the nip roller. The bottom surface of the outer layer is under micro-slip. At the edges of the contact zone, the surface is under slip and moves slower compared to the top surface of the layer beneath it. These slip zones reverse direction in the middle and between these three slip zones, two stick zones exist. In the slip zone in the middle, the bottom surface moves faster than the top surface of the later beneath it and in the stick zones, the surface velocities are equal. Due to this differential behavior in the tractions between the top and the bottom surface, a new traction exists in the top layer. This net traction when integrated through the contact width and summed with the web tension produces the WOT in center winding. In surface winding all the WOT is nip induced and hence, the WOT is equal to the nip-induced-tension (NIT). At low nip loads, the numerical results show that the WOT is approximately equal to ‘μ_Web/Web.N’ and at high nip loads, the WOT is much less than ‘μ_Web/Web.N’ where, ‘μ _Web/Web’ is the coefficient of friction between the web layers and ‘N’ is the nip load. Also, the results for the WOT and for the stresses in the contact zone were verified using experimental measurements.