Web ​Handling And Converting

In the last post we lamented the challenges of specifying roll length in the absence of industry standards.  With thickness we have the opposite problem:  too many standard measures.  Still, the results are the same:  the potential for a Tower of Babel communication issue.  To put this in perspective let me share with you an audit I did for one large company.  They had no less than 12 different ways of measuring or defining thickness.  Some lab tests differed in foot size or foot pressures.  Some were online.  Some were single ply, others multi ply.  Some were not even in the test lab or online scanner, they were in a product such as in-roll thickness.  Deferring to a standards organization does little to solve this because TAPPI alone has at least six thickness measures and there are many many more if we include other standards organizations.

Still, this does not get to two even more challenging issues that are almost never spoken of.  The next one issample size.  If you place any stock in statistics you will find that what you can ‘know’ about a lot or roll given a few lab specimens is surprisingly little (Frost, 1991).  The final challenge is that surprisingly few customer complaints come from thickness being too big or too little or out of spec.  Rather, customers complain that the wound rolls you supply look or perform poorly.  While it can be unsafe to apply generalizations to a specific situation, I will opine that a good share of these are profile problems in disguise.  By profile we mean the variation of thickness (or other property) across the width.  The great majority of bagginess (and related problems) and many wound roll defects are caused directly by profile or made worse by profile variation.  The problem is, however, we seldom have the sensors good enough to ‘satisfy’ the fussiest customer for level products, that is the winder.  In round numbers, at 1% variation of thickness you have few problems and at 10% variation you have few customers.  (Metals are tighter than that while blown film a bit looser because of 360 degree oscillation, but threshold of pain given here applies to many if not most webs).  So what’s the problem?  The problem is trying to find a sensor that can resolve thickness much better than 1% of your thin webs.  So, if we can’t ‘see’ the problem with our sensors then we are really handicapped in manufacturing and QA.  Fortunately, the wound roll tells you what you need to know in many cases about profile variation.

Come to my Web101 Web class for background and then get graduate training in Winding such as coming up inAugust 23-26 in Patterson NJ or as video-on-demand.  Then there will be little mystery why your thickness measurements will not always protect your customer from thickness related issues.

Over my career I have written more than one million words on web-handling.  I am releasing the material I own copyright to you, for free.  All you have to do is ask.  The better part of 40 years of experience and the better part of a million words.  Articles, blogs, columns, unpublished books and more.  All material is key-worded and searchable.  A read-me with FAQ’s will guide you to content and usage.  You can get this jam-packed folder of work in one of two ways only.


1)    Send me an email request with all of your business card information to DrRoisum@aol.com.  Please use “Best of Dr Roisum” in the subject line so that your request can get routed to the proper mailbox and department.  I will then send you a Dropbox invitation link that only you can use.  You must then copy that folder over to your own machine soon thereafter because that link will expire in 30 days.  Note, if your IT department does not allow Dropbox, you can do so on any other computer, such as a home computer.

2)    For US addresses only, you can snail mail (US Post preferred, Fedex, UPS etc) a SASE with a USBdrive/stick with at least 2 Gb of room for the files as well as your business card.  I will return the memory stick to you in your SASE.  For those not familiar with the term, SASE means Self Addressed Stamped Envelope.  Please make sure the envelope is padded and has sufficient postage pre-paid.

Please note that I can not process or even respond to incomplete requests.  Also, I can not provide material whose copyright is owned by others, so please don’t ask me.  Instead, ask the copyright owners directly.  The RoisumLibrary in the Best of Dr Roisum folder will guide you to the proper author and copyright owner.

Of course, if you want to organize your learning and make the process more efficient, there is no better way than to literally go to school.  These concepts and most other must-know aspects are covered in detail in my Web101Web and Winding Courses such as coming up in August 23-26 in Patterson NJ or as video-on-demand, both hosted by AIMCAL’s Converting School.  In-plant classes are another option that the majority of my 5,000 students have enjoyed.
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As always, I am ready, willing and quite able to help you troubleshoot your problems in your plant.  I have been to about 1,000 plants and have much experience that can help your team reduce waste, delay and customer complaints.  http://www.roisum.com/.

Roll length is whatever you measure it to be.  Since there are no industry standards, everyone is left to measure it in their own way.  Problem is, however, is that all will get a slightly different measure.  What is your response to your customer who claims they’ve been shorted?  The most common is to ‘pad’ extra length on your practices that are not reflected in the specifications.  Pad too much and you cost your company money.  Pad too little and you cost your company more money in claims and possibly lost customers.  So, how about a different approach?  How about studying why in the absence of industry standards you would get different answers about roll length?

There are two aspects to the problem.  The easiest is measurement.  The various definitions very roughly ranked (your mileage may vary as they say) from least to most ‘accurate’ (or more accurately, most repeatable) are:
Calculated (such as by Wound Roll Sizer app)

Number of sheeted products

Footage counter running on product

Idler roller rotations with target or tachometer

Driven roller rotations with motor tachometer

LDA (Laser Doppler Anemometry)

Complications beyond mere measurement are, well, more complicated.  However, they are explained in detail in my Web101 Winding course such as coming up in August 23-26 in Patterson NJ or as video-on-demand. 

How could something so seemingly simple be a cause for confusion and customer complaint?  It is because it is not simple if you take a close look at the figure.  Which width are you talking about:  slitter-slitter setup distance, test lab width, top of the roll width, middle of the roll width, what the customer measures width?  They are all slightly different as guaranteed by the laws of physics.  The test lab width is (usually) wider than the slitter-slitter distance due to Poisson necking through the slitter section.  Even the slightest web trough (lack of perfect flatness) going through the slitter section makes that difference even larger.  The middle of the roll must be wider than the top due to Poisson expansion from winding pressures.  (This can make stacking of rolls on ends problematic and even unsafe).  The customer may see yet different widths due to changes in moisture (paper and some polymers) or creeping in the wound roll.  There are other mechanical and control and winding upsets.  Finally add to this the occasional bleary eyed night crew operator checking setups with a ratty tape measure in a dim room and you have all the ingredients needed for a regular supply of customer complaints.  ‘Noncompliance’ may be errors less than 1 mm for paper or film to more than 1 cm on nonwovens, textiles and tissue.  (If you think you have it tough, in sheet metals we might see complaints for width errors the thickness of a human hair.)

So, how to cope?  It first begins by thoroughly understanding the physics of web and roll width as taught in my Web101 Web andWinding Courses such as coming up in August 23-26 in Patterson NJ or as video-on-demand.  Then you must do an audit and capability study as well as a review of customer complaints.  Finally, you may need to tweak a few procedures, specs or contracts to reflect your new understanding of how to serve your customer better in regard to a most common need:  web width control.

How can I measure length, slit width, diameter, position and/or printer registration on my web?


Dimensional accuracy of a web is so important that it usually specified by contract that also includes rejectable tolerances.  So, how can you measure things whose tolerances are less than 1mm (0.040”)?  Certainly a ruler won’t do it.  A micrometer, while accurate enough, is too clumsy to work in the plane of the web.  The answer:  an optical comparator.  This device magnifies about 100X so that 0.001” in the real world is 0.1” on the screen.  Newer computerized devices have edge detection and other features to make measurements fast and accurate and repeatable.  While the best of these could be as expensive as a new car, you can get entirely serviceable used ones on E-bay for the price of beater.  In any case, cheaper than a lost customer or customer return respectively.  There are many write-ups on the subject, but this on in the Quality Digest is one of the best.