Out-of-round paper rolls

Abstract

Paper is usually shipped in rolls covered by a thin wrapper to protect it from moisture and dirt. In effect, the roll becomes the shipping container for the paper. A single sheet of paper is weak and fragile, but in roll form it can withstand the substantial compressive forces required to lift it with clamps. However, even a small permanent deformation caused by clamping or impacts during transportation can cause a significant variation in web tension as the roll is unwound in a printing press. Tension variations can cause misregistration or flutter in a printing press. To compensate for out-of-roundness and the subsequent variations in tension, the operator will increase the average web tension, but that increases the chance of a web break. The ultimate solution is to make a paper roll that is resistant to the forces it will encounter between the winder and the printing press. As denser paper is made into longer and wider rolls, the force required to lift the roll increases, which may preclude handling by clamping. We have developed a mathematical model which shows that, for a given clamping pressure, the permanent deformation of the paper roll is related to the tension wound into the paper roll and the compressibility of the paper in the radial direction. The occurrence of out-of-round rolls can be reduced by tighter winding and using less compressible paper.