Web ​Handling And Converting

​In the past half dozen clips in this series we covered common bowed roller design and maintenance issues in detail.  In a few cases well beyond what we are able to do in our Web101 class.  (The last one this year in the US is Aug 23-26 in Patterson NJ).  Now we must end with a brief discussion of the challenges of integrating the man into the man-machine-material system called spreading.


Web201.44f – Bowed Roller Failure Modes – Other

https://www.youtube.com/watch?v=0UKuiZeubkA

***201.44f – Bowed Roller Failure Modes – Other

05 Slides Duration 02.31 v 15.08.28

201.44f.01 – Title Slide

Welcome to web handling.  My name is Dave Roisum.  In this final clip in a series we conclude with a few last failure modes for the bowed roller.

201.44f.02 – Other Bowed Roller Concerns

Sometimes it can be difficult to know when to stop.  We could go on for hours on bowed rollers.  So I will end with a final set of common troubles.

Teaching operators how bowed rollers work and how to operate them is not easy for good reason as we learned in Web101.  The bowed roller is one of the most complicated spreaders we have.  Still, this complication may be worth it because it is also one of the most capable of spreaders.
In fact, many engineers and even the bowed roller suppliers themselves do not know how bowed rollers work for the simple reason is that many do not read or go to school in all of the details they should know.

As I mentioned in previous clips and detailed in Web101, the bowed roller is not a trivial drive design and tuning application.  Then we have many maintenance challenges including cover wear and bearing failure, both of which can degrade spreading even when the cover is not obviously worn or the bearings still turn in some fashion.
Finally, when you get to speeds above a few hundred meters per minute, or certainly the thousands and even 10 thousand feet per minute the paper winder operates at, vibration can be devastating.  The bowed roller is a particular challenge here because, unlike most rollers, they can not be balanced.  Also, at least 3 resonances are inevitable in the speed range of paper machine winders.  Few builders can make a bowed roller good enough for high speed winders and none can do it without fail.

201.44f.03– Thank You
​
Thank you so very much for watching this module in my plant practical video clip series.  Stay tuned for more must-know topics in web-handling.

Bowed roller quality can be measured in many ways.  One is appropriately sized curvature (bow magnitude) that we cover in great detail in our Web101 class.  (The last one this year in the US is Aug 22-23 in Patterson NJ, though you can take it anytime as video-on-demand).  Another is a reasonably uniform curvature arc as we discuss here; perhaps the only time in the literature, internet or otherwise.  Putting these two quality metrics together we would have a uniform spreading profile.  In other words, the CD stress (unslit webs) or gaps (slit webs) would be consistent across the width.  If the average curvature is too high and especially if the curvature uniformity quality is poor, we can have the tendency to wrinkle at local lanes instead of spread.  The former is called ‘quarter-point’ spreading problems and the latter flat spots or kinks in the bow.




Web201.44e – Bowed Roller Failure Modes – Kinks in Curvature

https://www.youtube.com/watch?v=IRz3Br8SkEg

***201.44e – Bowed Roller Failure Modes – Kinks in Curvature

05 Slides Duration 03.24 v 15.08.28

201.44e.01 – Title Slide

Welcome to web handling.  My name is Dave Roisum.  In this clip we continue our series on bowed roller failure modes by looking at the risks of a bowed roller arc that has kinks and flat spots in it curvature

201.44e.02 – Concerns

Only certain applications are very sensitive to the quality of curvature.

Before slitter spreaders are relatively tolerant, but not so when you slit the web into lanes that must be separated.  Of course, the more lanes you have the more demanding is the system for curvature quality.  You only have a limited total spreading power and you want that distributed as evenly as possible.  Note, however, that gaps can not be even if the lanes are of different widths.  Wide widths automatically make wide gaps and vice versa.

Also, while you might imagine a kink to be more trouble, it is in fact the flat spot that is the much greater concern because there is no local spreading there.  Of course, for a given bow magnitude, if you have a high curvature kink there must be a corresponding low curvature flat spot.

201.44e.03 – After Slitter Applications

The practical concern is that tied up or stuck rolls is common in many industries, especially on two-drum winders or winders with a single shaft.

The practical problem is, however, that there are many totally different reasons that rolls could get tied up.  This is where knowledge of web handling plus experience with spreaders plus clever detective work must all come together.  Putting the right fix for the wrong problem may not be helpful.  Increasing spreading power may not only not help, it can in some cases make the problem worse.  In my web and winding classes we taught the necessary background to help troubleshoot this most troublesome problem.

201.44e.04 – Curvature Quality

The quality of curvature is an easy concept.  It is merely how close the actual arc of the bowed roller axle matches the arc of a true circle.

Yet it is in practice, almost impossible to see kinks and flat spots that might disable or destroy spreading.  Also, it is quite difficult to measure.  So difficult, that when I worked for Beloit as a winder designer we had to develop and teach the bowed roller manufacturers how to check this so that our equipment performed as well as possible.

As a final observation, the issues we discussed here are also equally true for other spreaders and, most especially, bent pipe spreaders.

201.44e.05– Thank You

Thank you so very much for watching this module in my plant practical video clips.  Stay tuned for the last clip in the series where we will just list a few final bowed roller failure modes.

A bowed roller needs room to do its job.  Crowding it toward either the upstream or downstream roller will have two possible outcomes:  (1)  poor spreading (2) the tendency to wrinkle.  Find out why.


Web201.44d – Bowed Roller Failure Modes – Crowding

https://www.youtube.com/watch?v=d7pHhkZLDtw

***201.44d – Bowed Roller Failure Modes – Crowding

05 Slides Duration 03.43 v 15.08.27

201.44d.01 – Title Slide

Welcome to web handling.  My name is Dave Roisum.  In this clip we continue our series on bowed roller failure modes by looking at what happens when you crowd a bowed roller into a small space

201.44d.02 – Bowed Roller Mechanics

Yet another surefire way to cripple or kill a bowed roller is to crowd it too close to the upstream or downstream rollers.  Understanding why this is requires understanding how the bowed roller works.

Recall from our Web101 class the mechanics of the bowed roller in bowed roller mode.  The streamlines or paths of different segments of the web are defined largely by the normal entry law that was also covered in our class.  These mechanics apply both to a full width web as well as a web slit into individual lanes.

201.44d.03 – Crowding the Upstream Roller

As we learned in our Web101 class, the ingoing section of the system is the ‘working’ section.  Reducing that span length by crowding the upstream roller reduces the amount of expansive spreading work available.

201.44d.04 – Crowding the Downstream Roller

As we learned in our Web101 class, the web must adjust from an outward directed path as dictated by the normal entry law to a parallel entry to the downstream roller.  If this is too crowded, two bad things might happen.  First, you may have to decrease the bow magnitude and thus reduce the amount of spreading.  Second, if you don’t and the path change is too abrupt, you can wrinkle.  Yes, as we learned in class, you can easily make wrinkles via poor spreader application and this is just one of many ways.

201.44d.05 – How small is too small?

How much span length is needed is impractical to model.  Thus we have to rely on not merely experience, but studied experience.  Studied means literally going to school and reading the papers.  Experience means seeing and recognizing failure modes under a wide set of circumstances.

The industry most at risk is the paper mills.  Not so much because they are not studied or experienced, because they are, but because they have packaging challenges far greater than other industries.  Because widths approach 10 meters, the L/W, or length to width ratios, are a crowded 0.1 compared to the more open 1.0 found in converting.  So, I will give a very crude guideline just for paper mills.  That is 1 foot is reckless, 1 yard is still risky except immediately after a coater where even that may not be nearly enough if hygroscopic expansion is high.

201.44d.06– Thank You
​
Thank you so very much for watching this module in my plant practical video clips.  Stay tuned in the next clip where we will describe yet another bowed roller failure mode that is particularly troublesome with after slitter applications, namely poor curvature quality.

Just as in core crush and telescoping and wrinkling and many other problems: curl is not curl is not curl.  In other words, curl is an outcome that has distinctly different root causes and cures.  In brief, the primary root causes are:

1. Simple laminator curl can be predicted with one of the free and easy AbbottApps.
2. One sided manufacturing.
3. One sided coating or converting (analogous to laminator curl)
4. Changes in environmental moisture + one of the above three
5. Roll-set curl

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Add to this the different directions:  MD, CD and chiral (diagonal or corner curl) and you have a recipe for disaster if people don’t due their homework.  In most cases, you must apply the correct remedy from a list that is based on the specific type of curl you have.

“To drive or not to drive, that is the question.”  This question can only be answered if you understand how the bowed roller works as we described in great detail in our Web101 class.  Also, this question can only be answered by knowing how the bowed roller does NOT work as was described in our class and outlined in the last clip.  However, just because you have a motor does not mean that the spreader will operate better.  In fact, a poor drive may well be worse than no drive at all.  Few people know whether a drive is helpful and how the motor must be programmed.  Here we will give you the clear answer.


https://www.youtube.com/watch?v=VvWdpB6BonA

 ***201.44c – Bowed Roller Failure Modes – Poor Drive Strategies

04 Slides Duration 04.19 v 15.08.26

201.44c.01 – Title Slide

Welcome to web handling.  My name is Dave Roisum.  In this clip we continue our series on bowed roller failure modes by looking at when and why and how a drive might be helpful as well as why a poorly tuned drive could make things worse.

201.44c.02 – Traction Circle

Last year I gave a half hour paper on traction as it affects the many spreader types and even more spreader modes.  The basic idea comes from a life-saving practice that all race car drivers and motor cycle riders and in fact every driver should know and practice to the point of becoming subconscious.  That is, you brake before entering a corner and when in the corner your hand or foot is on the gas just enough to counter drag and thus maintain speed.  More gas or more brake from this one special setting robs from total available traction and leaves that much less for the number one task of cornering, that is cornering.

201.44c.03– Available Traction

Perhaps the most important as well as least understood by the general practitioner is whether to drive a bowed roller and how to manage the drive setting if you do drive it.  Here I will give an abbreviated discussion of the why of drives.  The details of the how were given in our Web101 class.

The first case is when a combination of light webs and light wrap angles are coupled with a high bowed roller drag coming from the sum of bearing drag and cover hysteresis.  Here, the bowed roller will break loose everywhere across its width and the roller will either come to a stop or perhaps turn slower than web speed.  Here, bowed roller mode spreading is not possible.  Only bent pipe spreading is and that is an entirely different discussion.  Here we will just observe that it is a pretty expensive way to get bent pipe spreading and that you will quickly ruin the cover due to wear.

The second case is less severe, but a similar combination of light webs and wrap angle coupled with a high bowed roller drag, but not enough to break it loose entirely.  Here, the amount of available sideways spreading force is reduced.

The third case is optimum.  Here, a drive motor is provided and properly tuned such that drive torque precisely matches drag + inertia as we covered in Web101.  Here, all of the traction is available to do spreading work.
Finally, the fourth case is an improperly tuned drive that is common enough because most drive people don’t have web handling training.  Here, the motor overdrives and pulls on the web and causes a loss of spreading work because some traction is used up just tugging on the web.  In all cases of a mechanical belt drive slaved to some other roller, the drive will be less than optimum and quite probably worse than no drive at all except in extreme application cases such as tissue that must run in the bent pipe mode to due exceeding light tensions and tractions.

201.44c.04– Thank You
​
Thank you so very much for watching this module in my plant practical video clips.  Stay tuned in the next clip where we will show trying to jam a bowed roller into a cramped space can make things worse than no spreader at all.

My Web101 school was sold out at AIMCAL’s Converting School event in Milwaukee this spring.  For this reason another Web Handling as well as Winding course has been scheduled August 23-26 in Patterson NJ.
​
This is your last chance to get premier web handling training in the US this year except if you take the courses as video-on-demand training.  My last European course is November 22-24 in Stockholm.  This version is one day of web handling, one day of winding and one day of problem solving.  It is hosted by the Packaging Greenhouse for whom I have taught for more than a decade.

The most common of the three bowed roller operating modes requires traction.  Without traction everywhere and all the time the bowed roller might not just not spread, it might very well cause a wrinkle tendency.  There are many ways to lose traction; all of them design and application errors that could have been prevented by knowing the subject such as was taught in Web101.

Web201.44ba – Bowed Roller Failure Modes – Loss of Traction

https://www.youtube.com/watch?v=rCjWvQE8nYQ
​
***201.44b – Bowed Roller Failure Modes – Loss of Traction
04 Slides Duration 01.59 v 15.08.26
201.44b.01 – Title Slide
Welcome to web handling.  My name is Dave Roisum.  In this clip we continue our series on bowed roller failure modes by looking at the loss of traction.
201.44b.02 – Two Modes
As we outlined in a previous Web201 clip and as we detailed in our Web101 class, there are two modes of operation for a single bowed roller.  As we learned in Web101, there are also two modes of operation for a dual bowed roller system.
In this and subsequent clips in the series, we will primarily concern ourselves with the most common situation, a single roller in the bowed roller mode.
201.44b.03 – Slippage Begins at Edges
The most common design application error for the bowed roller is pushing spreading too far.  The result is problems at the edges where the edges are asked to move outward more than traction allows.  As we learned in Web101, they break loose and run into their neighbors that are still in traction resulting in the ubiquitous quarter-point spreading problems.  In Web101 we learned how to size bow magnitude as well as how to adjust bow orientation.  In Web101 we gave many slides on how to detect and avoid these most common spreading application errors.
201.44b.04 – Questions?
Thank you so very much for watching this module in my plant practical video clips.  Stay tuned in the next clip where we will show how a properly configured drive motor can improve spreading, especially for light weight products as well as how driving it poorly or not at all can degrade or even destroy spreading.