Effects of nip roller on wound roll stress distribution and friction forces (Simulation of winding process considering web wrapping around nip roller)

Abstract

How a wound roll stress distribution will change when a nip roller is used during winding, and how a wrap angle around the nip roller will affect the roll stress distribution, these are investigated by simulating a winding process of two-dimensional models composed of a web, winding core and nip roller using a FEM software. The results show that the roll stress distribution is classified into the following three groups, (G-I) no nip roller, (G-II) nip roller with zero wrap angle and (G-III) nip roller with non-zero wrap angle (90, 180 deg.). The roll stresses increase in this order. The stress distribution of (G-III) is almost the same even though the wrap angle changes. Macroscopic slipping patterns (like J-line) of wound rolls indicate that large friction forces due to a nip load pull the outer layers to the core rotational direction. A summation of friction forces acting on the web surface having contact with the nip roller is zero, when no external torque acts on the nip roller. This indicates the stress distribution of (G-III) is almost the same. The friction force (the slipping velocity) is generated by a strain increase due to the wrap angle and a V-shaped tangential strain distribution due to contact with the nip roller.