Friction Characteristic
Dynamic slip behavior that varies according to processing speed determines the grip of paper webs on moving rollers. With rate dependent traction, the coefficient of friction between the paper substrate and the steel roller changes as the speed of the converting line increases. This behavior dictates how tightly the web is held during rapid acceleration and deceleration.
High Speed Behavior
Air entrained between the fast-moving paper and the solid roll surface creates a microscopic air bearing that reduces direct contact. Because of this layer of air, rate dependent traction tends to decrease at higher machine speeds, which can cause web slippage or wandering. This loss of contact impairs register accuracy in multi-color printing presses and can lead to uneven tension profiles.
Specialized rollers with grooved surfaces or textured coatings are utilized to bleed off this trapped air and restore stable traction.
Web Tension Control
Maintaining constant tension requires continuous torque adjustments on the winding and unwinding reels. If traction drops suddenly during a speed increase, the web may slip, causing tension spikes that lead to paper breaks. This makes predictive control software necessary to adjust the drive speeds based on the speed of the converting line.
