WebHandlersQuiz #17: Winding at Constant Torque

Published: July 27, 2012, By Timothy J. Walker

WebHandlersQuiz 17 continues the Q&A format I began this past February with our quest to address fundamental questions concerning web handling. To see past Quiz questions and answers, visit: pffc-online.com/blog/walker. 

So this blog posting focuses on Winding—If you center wind at constant torque, what is the percent of change in tension if the roll diameter changes from 100 mm to 400 mm?

Constant torque center winding applies a constant torque in units of force times distance (e.g., lbs-in., N-m) to the center of the winding roll. This torque is converted into tension based on the distance, which is the radius, to the outside surface of the winding roll. The actual radial value is as important to this question as the ratio of the radial change – 1:4. If the torque value is initially divided by 1 to get a tension and later divided by 4 to create tension, the final tension will be 4:1 or four times lower.

If the starting torque was 400 N-mm, the initial tension would be (400 N-mm)/(100mm) = 4 N. At the final radius, tension would be (400 N-m)/(400mm) = 1 N; so the tension would drop 4x.

Stay tuned to this blog for more Q&A. My next Quiz will feature another facet of Winding involving internal roll pressures of paper and film products.