The following is historical fiction. One where certain essential details are accurate, but the ‘conversation’ has been rewritten to protect the guilty.
Dear Dr. Roisum,
I was your student in a Converting School back in 20__. We now have a difficult web-handling problem caused by baggy web. We have to cut down the cost of our products, so we tried cheaper film supplied by a new company.
It appears foolish to try to 'save' money by going to a cheaper film supplier,
especially since the result has now proven itself as increased waste/delay due to bagginess,
especially since that film is so readily available from many sources and generally quite flat
especially since the product you make, _____, is so demanding
But new film has a baggy web problem. Its thickness is 38 micrometers. The thickness variation is ONLY [my caps for emphasis] 0.6 micrometers, almost same as the one that we usually used.
The 0.6/38 thickness variation is 1.5%, which is only ‘ordinary’, not necessarily ‘good’ and certainly ‘not good enough’ for you as evidenced by increased baggy troubles.
We tried to do “strip test” that you taught me. As a result, we found there was a 0.1% length difference despite using the center cut roll. We thought the length different caused the baggy problem.
A 0.1% (1/1,000) is not even ordinary, it is a gross variation in almost any application. Even so, strip test measurement is time-consuming to do accurately. Have you tried a roll hardness measurement such as the Paro-tester to see if it is predictive of bagginess?
The workers adjust the alignment of a roller to keep away from a baggy problem. They ask me about easier solution.
I would NOT misalign rollers to adjust to bagginess. Rather, I would optically align your machine so that you do not contribute to the problem. If it is absolutely necessary to skew a roller:
only a roller or two in front of critical processes such as a coating roller
have a micrometer adjustment capable of 10 microns per 'click'
have the micrometer zeroed to 20 microns so the operators can get back to home
In the seminar, you taught me “I Roller made by METSO”. But I couldn’t find the information. Could you tell me more information?
iRoll and IQ tension systems cost on the order of $100,000 and are far more expensive than just buying good film.
Any tips on how to handle the bagginess in this case, especially equipment?
You have probably tried everything reasonable; good tension control, effective application of spreading; precision alignment of your own equipment. You really are left with two basic choices
Return to a film supplier that can supply flat material
Accept the extra waste/delay caused by baggy material
Tell me some other papers or books about this problem.
You already have a nice module on wrinkling from my Web101 class. There is a baggy web article you can download from my website. Finally, I attach a module on baggy web troubleshooting (AIMCAL AWEB 2008) that you can pass on to your supplier with the warning that if they can't get the problem fixed, you will go elsewhere to get a flat product.