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Filed under: Guiding, Spreading, Wrinkling --- Tim Walker @ 06:30 PM

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

Filed under: General Business Topics --- Tim Walker @ 01:49 PM

Though convertingblog.com is necessarily designed as a ask-the-experts site, we are happy to take your questions. Often the best blog posts have been in response to questions I've gotten from clients or blog-visitors. So ask away.

One caveat. Question will obviously become part of our growing database of converting knowledge. Sharing information is the whole point of convertingblog.com.

What to contribute with an answer? Please do. If you tripped along something that solved a problem - share it with us. Maybe you've found a solution to something, but don't know why it works, or maybe it doesn't work all the time. We'll try to help.

So ask and post. We're interested.

tjw

Filed under: Tensioning, Web Mechanics --- Tim Walker @ 09:38 AM

What is the best tension control plan for processes that start and stop frequently?

The biggest problem with stopping and starting is inertia and coordinating motor speeds, especially for the unwinding and winding rolls. Inertia time acceleration (or deceleration) creates a torque (at steady speed, there is no accel, so no torque). The inertial torques of rolls or rollers can easily be many time the torque of tension (times radius of the roller) or other torque losses (drag, etc.).

Any tension control plan must answer four questions:
Q1. How will I apply torque to the web to create tension (motor, brake, clutch)?
Q2. How many tension zones will I have in my process?
Q3. Which drive point will be my master or pacer drive (the motor that is in speed control, no tension loop)?
Q4. How will I trim the torque or speed of the follower sections?

Stop start may affect all of these decisions.
A1. Regenerative motors (motors that can function in power or braking mode) can be programmed to respond to predicted inertial loads, reducing tension upsets.
A2. The number of zone you need may go up with high inertial torque from a process with a large number of rollers.
A3. You need to ensure that the pacer section doesn't slip. The inertial loads of stop-start processes can create surprising tension changes within a zone and across drive points. Becare to estimate the tension swings from inertial loads when determine the friction needed at the pacer drive point.
A4. Dancer rollers do a great job of forgiving speed errors between pacer and follower sections. For intermediate tension zones, where the master and follower are controlled by rollers (with constant diameter) and a line speed reference signal is used to set the follower's baseline speed, a transducer roller is usually good enough to feedback web tension. However, on unwinds and winders, where diameters are changing, a dancer roller is a good alternative to forgive the more likely speed errors created by roll diameter uncertainty.

Lastly, for any process, I think it is a good idea to include a 'stall' mode in the process. In this mode, the line first pulls the web taut at zero speed before shifting to accel and run mode. The stall mode ensures a smooth transition from stopped to running conditions.

This all said, the slower you accel/decel, the less these issues are a big deal.

Filed under: General Business Topics --- Tim Walker @ 06:02 PM

AWEB is around the corner, the new Applied Web Handling Conference sponsored by AIMCAL. I've had my fingers deeply into this conference from it conception.

AWEB-IWEB controversy? What controversy?

It's seems some of the folks involved with IWEB (the International Conference on Web Handling, sponsored by Oklahoma State University's Web Handling Research Center) have some hard feelings about this new AWEB conference.

I wish they didn't feel this way. I view the AWEB conference as a complementary effort to the IWEB conference. I've felt this way since before AWEB was even on the drawing board.

I've attended the IWEB conference for years, starting in 1991. It's a great conference. I've learned a great deal about the most advanced work in web handling, with many papers covering work at the PhD or Master's engineering thesis level.

But after attending IWEB for many years, I felt there was room for something more, something that would help bring the advanced concepts down a notch to the applied level. While at 3M, one of my jobs was to learn something from the advance research at the WHRC and figure out how to apply it to make better 3M products or processes.

I feel that there is a great appetitie to help more engineers understand how to apply the advanced concepts of IWEB and similar advanced or academic resources. In the post IWEB conference discussion sessions in 2003 and 2005, I advocated for IWEB to expand and find a way to address this need. Alas, IWEB is quite successful and being so doesn't always create the driving force for growth or change.

In comes AIMCAL and their interest in a possible applied web handling conference. AIMCAL has been sponsoring web handling as part of their summer school program and held technical conferences for many years on topics of coating, drying, metalizing, etc., often with a equipment supplier's POV, but open to others.

I jumped at the opportunity to help AIMCAL get this concept off the ground, something that the WHRC seemed to have little interest (at least little action) in pursuing. That said, very early in the AWEB planning process, I contacted Dr. Karl Reid, the WHRC Director and invited him to the table, seeing an obvious win-win situation for these two conferences to complement each other.

How IWEB and AWEB work together?

IWEB - Advanced web handling papers, aimed at top web handling experts of academia and industry, held in odd-numbered years at OK-State Univ.

AWEB - Applied web handling papaers, aimed at the next tier of the web handling technical community, held in even-numbered years at a rotating location.

The idea is for AWEB to fill a niche. In business, it's called the loose brick theory. When you go into a market, don't go at it's strength, don't try to compete with the strongest product out there. Go where the market has a need. If the product is web handling technology transfer, the high and low end are strong bricks.

IWEB is the premier, Lexus-BMW of WH technology transfer. There are tens or hundreds of engineers looking for this product.

There are many Kia-Hyundi, fundamentals seminars for web handlers. There are thousands to tens of thousands of technical folks needing this product.

The loose brick is the middle of the pyramid, the Toyota-Chevy product, something between fundamentals and advanced. What we are calling applied. There are hundreds to thousands looking for this product. We hope to bring it to them.

So what controversy is there? I hope none. I think some IWEB folks saw the new conference name, AWEB, and found it too close. That imitation wasn't flattering. From there, it's easy to see what you want to see and hear what you want to hear.

For the few of you in this camp, it's probably hopeless to convince you otherwise, but please give AWEB another look and realize that this new conference is an opportunity to grow the web handling community, including driving more people up from the Toyota product to the Lexus product.

I hope this isn't too much of a rant, but I feel strongly about smoothing the waters of the web handling world.

tjw

Filed under: Rollers, Traction --- Tim Walker @ 11:14 AM

Practical, applied web handling knowledge...

This is the intended product of the AWEB conference next month in Charlotte.

I'm busy getting my slides ready. I've got two presentations and a half-day class going on. Here's some background on pulling together the plan for the first presentation I'm working on. It's outcome of a nice three-way collaboration.

Presentation #1 - Measuring pressure in rubbber-steel nip roller systems.

What do you get when you combine precision diameter measurement with a thin film pressure sensing system?

I've know Steve Huff at Abba for many years through his alway informative presentations at AIMCAL's Fall Technical Conferences. Steve gave me a tour of the Abba facility, including their LMS 3000 precision diameter measurement system.

I met Vin Carrara of Tekscan in November when he was on a sales trip to the Minnesota area. I've know about the Tekscan system for many years and new it can be an effective tool for measuring nip pressure variations.

Sometime in December, we were planning the AWEB conference and I thought..."wouldn't it be great to see these two devices, the diameter and pressure measurements, put together in an AWEB paper." Well, a couple emails and a few phone calls later and we had a plan.

Each team member brought something to the table:

Abba Rubber, design and built the nip test stand and rollers and volunteered Steve's time and the LMS 3000 use.

Tekscan, provided the Tekscan sensors, software, and computer, plus Vin Carrara time and travel to Ontario, CA

TJWalker + Asso., mostly, I played Hannibal Smith to this A-Team, but also donated my time and travel to Ontario, and completed the data crunching and slides with my XLS and PPT skills.

The result: I'll post more hear after the AWEB conference.

Filed under: Tensioning, Web Mechanics --- Tim Walker @ 10:57 AM

Here's recent question:
Is it better to control tension and let strain fall where it may or control strain at whatever tension is necessary?

TJW Answer:
This is a big question, but let's try to answer it simply.
Most webs are elastic, so controlling tension or strain are really the same thing. If you have a web with an elastic modulus of 500,000 psi, then 0.5 lbs/ in / mil will be 500 psi stress or 0.1 percent elongation. It doesn't matter whether you run at 0.5 PLI per mil or 0.1 percent strain.

(All webs should be run at an average stress or strain that is 10-20 percent or less of their yield or break point.)

However, sometime things are not elastic.

For crepe paper, such as used to make masking tape, you can pull with too much strain and pull out the crepe, never to be recovered. This is a bad thing since the masking tape user is paying to get that strain for their conforming tape application.

In making nonwovens, before the binder is applied and cured or dried, the fibers can easily be pull out changing the product thickness, porosity, or other property. Overstraining the material is a bad thing.

Some webs are viscoelastic. If you pull on vinyl tape, it will stretch more every second or minute you keep the load on it. To avoid this, control strain, not tension. I was recently asked if web handling applied to cookie dough. Yes, but you better thing about the time - tension material property, the viscoelasticity of the dough.

Bottomline answer:
For most product, controlling tension, the easier to measure property is normal and let strain fall where it may.
It's still good to know what your typical web strain, because as I wrote my recent article in PFFC, strain is the secret to web handling. Strain determine specs for roller alignment, diameter variations, speed variations, etc.

For those special products that yield easily or are highly viscoelastic, look at controlling strain.