- Keith Hevenor
Editorial/Conference Director
CMM International

Once the distinctive patterns of wear are classified, the solutions will be easier to recognize and implement without resorting to "taking a stab in the dark"' or applying an unnecessarily costly solution to a relatively simple problem.

As part of the management team, I know that my views are biased on this topic. When we (PennWell) first acquired CMM right after the 2005 event, we knew we faced an uphill battle. The previous management had steered the event badly off course, and it had been on a downhill trend for a number of years. However, in speaking extensively with experts in the industry, the consensus was that the brand remained strong and the potential for turnaround was great. Almost without exception, everyone we spoke with told us they wanted us to "fix it."
The number-one request from those we surveyed was to have more running equipment on the show floor (also referenced in the Converting Blog posts from 2005). By implementing the two new Technology Centers in 2007, we not only added more running equipment, but did so in a way that showed attendees the equipment producing actual jobs in a live production environment, demonstrating real-world workflow and integration issues. In addition, we worked with Rosemont Exhibition Services to make it much more affordable for all exhibitors to bring equipment to the event. The result was a floor filled with running equipment (more than 1.5 million pounds of it!).

Our other objective for CMM was to improve and increase the marketing efforts that draw high-quality attendees to the event. With the confidence that comes from having listened to the industry and focusing on delivering value, we were able to aggressively promote the new features of the show and the advantages of participation rather than spending our time knocking other events. The success of CMM is our only goal, while the failure of any other events is irrelevant.

The feedback we have received from exhibitors has been extremely positive. Almost all complimented us on the quality of the sales leads and the energy level on the show floor. Nearly 7000 converting professionals made their way around the floor during the four-day event, more than in 2005 but fewer than in the heyday of 10 or 15 years ago. What we are seeing is that converters are sending fewer employees today because of tighter travel budgets and leaner workforces--but those who do come are the decision makers and executives, not just the tire-kickers or employees looking to get out of the office.

PennWell is a 100-year-old, family-owned company that publishes 45 magazines and runs more than 60 highly successful conferences and exhibitions around the globe. It invests for the long term and leverages its expertise and resources to be #1 in all markets it serves. CMM is no exception, and over the next two years, you will see a lot more of CMM in the market. Our goal is to make CMM a year-round, 24/7 industry resource, offering web news, e-newsletters, webcasts, product guides, and a variety of other features that help converters do their jobs better, smarter, and more productively.
Let me (and the converting community) know what you think. I don't expect or want to hear that we did everything right--in fact I know we didn't. But we did learn a lot, and I feel like we've put CMM back on track and we're excited to do even more moving forward.

Keith Hevenor
CMM Editorial/Conference Director

How about putting it another way? If you have a choice of developing a new Excel spreadsheet (or other computer program) or modifying a spreadsheet someone else has written, which is easier?

It is almost always harder to work on something that someone else has started. It was hundreds of years between the beginning of manufacturing processes to the creation of the assembly line. Having to modify someone else's work requires an initial step of figuring out where they left off. When you do a job yourself, you know what's been done (unless you put it on the shelf for too long, then it's like starting over).

Let's get back to registration.

Whenever possible, always integrate multiple printing, die cutting, and laminating steps in a single process. It may seem that creating a complex integrated process will lead to more waste (it often does), but in the case of registration, a great deal of startup and process variation waste is actually reduced by integration.

More...

In running a multi-color rotogravure press, if we have different diameters in our impression roller in different printing units, maybe having variation of maximum up to 3mm in the circumference, because some of the impression roller have been ground once after too much wear.
1) Does it effect the tension in the web?
2) Will it lead to registration problems?

Answer:

My expectation is that the impression roller diameter variations will cause some tension variations, but not necessarily cause registration problems. The answer to why I think this is somewhat complicated, but here's my thought process, in brief.

Multi-color presses typically run in draw control with either a mechanical or electronic drive shaft to synchronize the rotation of the variation printed patterns. In draw control, the tension is determined by the incoming tension (from the unwind) and the speed ratios of the other drive points. Impression roller circumference or diameter variations will directly create speed variations. A 3mm circumference variation on a 10" diameter roller (250mm) would have a speed variation of 0.4 percent, which is a large amount for most papers and films and would create a tension variations.

However, in rotogravure, the inking nip is not necessarily a no slip process. The ink-lubricated gravure cylinder is able to slip (on a microscale) relative to the web, but since it is driven with the lineshaft, all the printing pattern stay in synch without any major effect of small variations in tension goes up or down (talking here about tension offsets present in the steady state, not tension oscillations over time).

-tjw

In our operation for 8 color rotogravure presses, sometimes the pressure in the printing unit nip area varies on both sides of impression roller resulting in the wrinkles/misregistration. To eliminate the problem, we balance the impression roller by different mechanical methods and run the machine. However, we only discover the problem once the machine runs.

Is there anyway of checking the balance of nip pressure on both sides at each printing unit nip, maybe with the help of some mechanical guage putting between the cylinder and impression roller on each side and applying the pneumatic pressure?

My answer:

There are simple and complex ways to measure nipping roller uniformity. Almost all are static measurements, so they don’t indicate variations over time or differences through the roller rotations (unless you take multiple measurements).

The first option many people use is to measure nip footprint length (sometimes called width) in the machine direction. You can measure nip width by inserting Post-It ™ notes from either side of the closed nip, then open the nip to measure the gap between the opposing notes. Many people use knurled aluminum foil (called Sto-Foil) from Stowe-Woodward. There are other nip footprint measuring options, including carbon paper, Fuji Prescale film (sold as Pressurex by Sensor Products), and electronic thin film sensor options from Tekscan and Sensor Products.

Force can be measured indirectly with a frictional device (made of a brass-steel sandwich) and a force gauge or with the Tekscan or Sensor Product devices.

You could also consider installing a load cell in your nipping assembly to measure the force exerted by any external air cylinders (and assume roll weight is constant).

I recommend nip sensing products from both Tekscan (www.tekscan.com), and Sensor Products, Inc. (www.sensorprod.com/nip.php)

I would recommend first trying simple nip width measurement (like the Post-It or carbon paper methods) or the frictional brass-steel system.

-tjw

Definition: Center winders drive a roll from the core or center. Surface winders drive a roll a nipping roller in contact with the roll's outer surface. Center-surface winders do both, driving the roll from a combination of center and surface driving.

The inquiring party makes several good points / questions:

> Center-surface winding makes some sense for very slippery (low web side A to side B coefficient of friction) webs.

Yes, this is to avoid how much torque needs to be transmitted through the roll.

> The bottom line on wound roll tightness is the wound-on-tension and the profiling of the WOT versus the roll diameter (a.k.a. WOT and taper tension).

FYI, WOT is the tension of each layer as it is added to the winding roll) and is a function of applied center torque and winding nip load.

> A center winder with nip pressure control can achieve a large enough range of WOT to wind most everything.

Yes, I agree again. The paper industry (and other LARGE roll winders) use surface winders since torque is independent of roll diameter. Center winders can be limited if the core to final roll ratio is too high (a.k.a. the buildup ratio).

> Why do people 'need' the extra complication and cost of a center-surface winder?

I think of most center-surface winders as surface winders with center assist. Surface winders can have trouble getting the initial layers near a core tight enough and the center assist can help with this. If you want to wind an ultra-soft roll, say a nonwoven or tissue product, your surface winding can only go as soft as the nip load required to turn the core, core shaft, and bearings. If you have a center assist, you can go to lower nip loads and softer rolls.

> What does the addition of the last 'T' knob (in TNT) give you besides more variables to mess-up?

Yes, may people that buy surf-center winders never figure out what to do with them.

There has been some interesting work out of Oklahoma State's WHRC how different nip rollers change the tension induced from the nip roller, but it's still all about modeling a roll from a given WOT vs. diameter. I think there is work yet to be done on how WOT from tension and WOT from nip may magnify or de-magnify crossweb roll variations from crossweb caliper and roll diameter variations, but I haven't seen any good work to point anyone in the right direction.

Conclusion: Use winding technology appropriate to your application. Don't get more knobs if you don't need them.

-tjw

This web handler knew the theory that spiral tape has no spreading effect, but wanted to know how to battle the strong local opinion that the tape spirals were required to prevent wrinkles.

My reply:

What can I say about helically wrapped tape on rollers? I’m not a fan and yes, Ron Swanson of 3M proved (and presented a paper at IWEB in 1997) that there is NO SPREADING from spiral tape.

So why is it popular? It there something more happening than the pleasing and mesmerizing optical illusion? I think ridged rollers, either ridges formed by the gap between spiral tape bands or the ridges of one tape banded stepped on top of another, can have a wrinkle disturbing or wrinkle dispersing benefit. If the unwrapped roller is prone to wrinkles from the combination of traction, misalignment, diameter variations, baggy web in long spans, or other wrinkle sources, then the spiral tape can help by turning a tendency to form one big creasing wrinkle into several smaller non-creasing wrinkles.

Do I like spiral tape or recommend it? No, but it may seem like the easiest way forward.

My preferred plan of attack is the same as the person who sent this question.
1. Remove the tape and see what's up.
2. Diagnose where the wrinkles are forming, starting with the first, most upstream wrinkle.
3. Look for the tale-tell signs of shear wrinkles caused by poor alignment (diagonal troughs and walking wrinkles).
4. Measure and maintain alignment.
5. If wrinkles persist in a few locations (rarely do all rollers have wrinkles), try using masking or similar tape to create a concave roller with a percent diameter variations appropriate to the web strain.
6. If concave rollers don't work, feel free to try your favorite spiral tape pattern.
7. If you want to eliminate all tape on rollers, which is a great idea for contamination-sensitive products and for an operator-independent process, there is more hard work ahead, but it can be done. This harder way forward includes work towards optimized traction (wrap, tension, and traction coefficient), optimized span lengths, reducing bagginess, and tactical use of concave rollers.

The best argument against tape is contamination. If tape is left on a roller long enough, eventually you see small pieces missing. Where did they go? Off to you customer and won’t they be happy!?

tjw

For an update on this story, check the comment below:

It was nice to have some live input from what can otherwise by a low interaction experience, blogging, that is. In blogging, you post and....nothing. Where's the immediate gratification. There isn't any. It's like writing a book. If you write email, you get replies. If you write a magazine column, at least a check comes in the mail and you see your writing in the magazine when it comes in the mail. But blogging, is hard to feel the reward, especially when I'm just writing about what I've been thinking lately. It's much more fun when this blogging thing is more a dialogue and less a monologue.

So my request to you convertingblog.com readers is PLEASE send me some questions.

If you set web tension from an air pressure gauge, there are two likely possibilities of what you are doing. If you have a dancer roller, you may be controlling the air pressure to one or two air cylinders that apply an external force to the dancer roller. If you don't have a dancer roller, the air pressure is likely going to a pneumatic brake or clutch, setting the slipping torque transmitted to the unwinding roll, winding roll, or a torque-controlled roller.

In either case, I highly advise spending some time with a force gauge (like a fish weighing scale) and measure the relationship between the air pressure settings and web tension.

[This entry is part of a growing 'book' that I am writing and posting at www.webhandling.com. Convertingblog.com is getting an exclusive first look at this restricted material.]

Rubber is the classic example of an elastic material. You push on it, it deforms; you let go, it bounces back. An elastic material responds to load almost immediately (the load travels through the material at the speed of sound). The amount of deformation is proportional to load and independent of time.

Definition: Viscous is the property of having a relatively high resistance to flow.

Molasses is the classic viscous material. When a force is applied to a viscous material, it will flow. The longer the load is on the viscous material, the more it will flow. When the force if removed, they stop flowing, but won't recover.

Definition: Viscoelasticity is the property of having both viscous and elastic properties.

When a viscoelastic (V-E) material is loaded, it will respond with a mixture of viscous and elastic behavior. Upon loading, a V-E material will immediately stretch (elastic behavior) and begin to flow (viscous behavior). When the load is removed from a V-E material, it will recover, some immediately (elastic behavior) and recover more over time (viscous behavior). Vinyl electrical tape is a classic and easily observed V-E material.

Do this test yourself. Pull out a 2-3 foot length of electrical tape. Hang a 1-2 lb weight on it. Note the initial elongation and that the tape will continue to elongate. Take the weight off. Note the initial recover and ongoing recovery.

Congratulations, you've just completed your first creep test.

[This entry is part of a growing 'book' that I am writing and posting at www.webhandling.com. Convertingblog.com is getting an exclusive first look at this restricted material.]

A: I don’t have a strong preference on horizontal vs. vertical, but I am strongly in favor of pivoting dancers over linear dancers.

I prefer a vertical dancer arm with horizontal motion so that gravity is perpendicular to the tensioning direction, but make sure the dancer arm is hanging (as opposed to standing) with the the pivot point above the roller. Hanging dancers are 'sloped' to run stable; gravity tends to pull the roller back to its null position. Standing dancers, with the pivot underneath the roller are destabilizing with gravity trying to pull the roller away from neutral position.

My preference for pivoting over linear is based on observation of friction and sticking almost always higher in linear systems. If well-engineered, there is no reason a linear system can work great, but too often a linear dancer has more trouble holding its alignment, creating tension variations and wrinkles. A pivoting dancer can also be poorly engineered, but you have a better change to get low friction in a rotary bearing and simple structural design can translate a well-aligned pivot shaft into a well-aligned roller.

-tjw