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June 24, 2005
Draw Tension and Web Width
John Bastarache wrote in with an interesting question:
"I have a question about tension in the sheet. If a sheet is 100 inches wide and trimmed down to 80 inches wide, is there more tension in the sheet at the reduced cross direction of 80 inches. Keeping in mind, that the draw is a constant."
If the tension was created by a dancer roller or applied torque, then the tension would increase on a PLI (pounds per inch of width) or psi basis.
However, you've included that the tension is created by draw. If you read my last two columns from a pffc-online.com, you'll learn the fundamentals of draw control. Draw creates tension through the web's material property, modulus, relating stretch (or strain) to stress (or tension).
Tension (lbs/in) = strain x thickness (in) x modulus (psi)
Therefore, the tension created by stretching (or drawing) on a force per width basis is independent of web width. However, if you are wondering about the total tension force (lbs), this will go up with width.
Force of Tension (lbs) = strain x thickness x width x modulus.
You can think of the t*w*E (thickness x width x modulus) as the web's spring constant.
Posted by Tim Walker at June 24, 2005 11:58 AM
