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April 30, 2006
Can a Thinner Web Wrinkle Less?
I was crunching some number this weekend on tension, misalignment, and shear wrinkles. (I know...exciting weekend...but it was raining.)
Did you know sometimes a thinner web is LESS sensitive to roller misalignment and shear wrinkles? It goes against intuition, but it is backed up by theory and experiments (most of these out of OK State Univ and their WHRC).
For example, what misalignment creates a wrinkle for 48" long by 24" wide span, polyester web with modulus of 640kpsi? Tension is 1 PLI and thickness is either 0.5 mil or 1.0 mil.
Surprisingly, the 1.0 mil wrinkles at a misalignment of 15 mils/ft and the 0.5 mil doesn't wrinkle until 18 mils/ft.
Why would the 0.5 be less wrinkle sensitive?
My lateste saying is "What is the secret to web handling?" The answer: strain.
That's why 0.5 mil at 1 PLI is less sensitive to misalignment than 1.0 mil. The 0.5 mil is at twice the strain at that tension. More strain means more stiffness and less percent stress variation from the same misalignment.
If you look at the 1.0 mil sensitivity at 2 PLI, at an equivalent strain to the 0.5 mil at 1 PLI, the 1.0 mil now wrinkles at 26 mils/ft. So once you compare the two thicknesses at equal strains, you see the benefit of thickness.
Just one of many tidbits will be giving out at the AWEB conference Wed. PM short course on wrinkling. Hope you can make it.
tjw
Posted by Tim Walker at April 30, 2006 06:30 PM
