Closed solid-state-fluid mechanical model for calculating the transferable torque on wrapped rolls

Abstract

Higher velocities of webs at the same or reduced web tension require basic improvement of the existing machine technique. Concerning the transferable torque between a web and a roll common work is restricted either to the foil bearing theory at constant web tension without solid-state contact, or to the solid-state friction, including in some cases the influence of a constant fluid pressure. In this paper a model for calculating the transferable torque between a roll and a web is introduced which is more conform to reality. In the web mounting and in the web launching area the gap width and the pressure are calculated taking into account the web tension. In the intermediate area, where contact occurs between the rough surfaces of web and roll, it is assumed that the gap width can be substituted by an equivalent gap width between smooth surfaces. The transferable torque is calculated taking into account the local fluid pressure. The calculations show that, in the contact area, the compressibility of the fluid has a significant influence on the pressure profile and, finally, on the transferable torque.

A device reducing the air entrainment by means of the so called "gap throttle effect" is introduced. It needs no separate energy, works nearly without contact, and has our patent pending on it. The maximum velocity up to which torque is transferable, as well as the transferable torque at a constant velocity, can be increased by this considerably. The effectiveness could be verified at a test rig in our laboratory.