Influence of the gap throttle effect on the winding process and roll quality

Abstract

In the paper industry the winding technology has a significant influence on the quality of finished rolls. The rising productivity and quality efforts require a constant optimization of the winding process concerning the winding speed, the damage-free structure of the wound rolls and the appropriate transport stability. The air between the layers of the roll negatively affects the achievable quality. Up to now, grooved or nip rollers were used to avoid air entrainment. These principles were proved to be insufficient at high winding speeds in their operation limits.

The innovative application of a gap throttle foil reduces the air entrainment to such an extent, that a higher contact pressure between the incoming layer and the roll is reached. In this work the performance of the gap throttle effect during winding was theoretically investigated. A simulation tool, which calculates the inner state of stress in a wound roll under different process parameters by the use of a gap throttle foil, was developed. Especially the influence of web tension, web speed, roll radius, gap throttle foil thickness and immersion depth are considered as parameters. Furthermore additional elements like contact rollers to support the gap throttle effect are investigated.

The results prove, that the effect can be used to achieve higher radial tension in the roll. Subsequent investigations show, that the effect amount and its stability can be increased considerably by an additional small pressure on the web surface at the mounting area of the web. This novel principle for winding machines should be investigated furthermore, because without niprollers, a paper friendly winding process and a winding quality comparable to the 4uality of center-surface winder could be realized.