Web Lines | Wrinkling?

Can we predict differences in wrinkle sensitivity of different products?

Wrinkle models can help. They can look at your product geometry, mechanical and frictional properties (of your rollers), roller factors, web path geometry, and process conditions (speed/tension), then predict wrinkles from roller misalignment, roller diameter variations, and roller deflection. But, models have their limits, especially when you use them outside the window of conditions where they were verified. This is called extrapolation and will often get you in trouble. In finance, they call this "Past results do not predict future performance."

How do you avoid the pitfalls of extrapolation? Do your own experiments. Wrinkling experiments are not overly hard. They can be time consuming, if you want to test a variety of webs, rollers, and process conditions, but they are speedy quick compared to winding trials.

Here are three wrinkle mechanics that can be tested with a fairly simple equipment setup.

  • Wrinkles from misalignment
  • Wrinkles from roller deflection
  • Wrinkles from nipped rollers

It is important to think about the wrinkles you have in production and which of these tests would best predict helping to reduce your specific wrinkle causes.

shear wrinkles

The standard set up for shear wrinkles is an adjustable roller with 90-deg of wrap and entry and exit spans of at least the web width. The adjustable roller has micrometers on it to measure the misalignment. The adjustment should be parallel to the entering web span and perpendicular to the exiting web span. We want wrinkle-inducing bending on the way in and gentle twisting on the way out. The adjustable roller should allow for changing the roller to test different roller types. The roller upstream of the adjustable roller should have good traction, such as wrapping it with rubber tape. In shear wrinkle experiments, the angle to create a wrinkle is plotted vs. tension (or speed/tension ratio), and repeated for different webs, roller, speeds, etc. Smaller angles to wrinkle means more sensitivity. This test should create an all-too-familiar angle trough and wrinkle "walking" across the misaligned roller.

ROLLER DEFLECTION WRINKLES

For roller deflection wrinkles, design and build a series of rollers, maybe just two or three, with different deflection behavior (like small vs. large diameter, thin vs. thick roller wall, or aluminum vs. steel). Set up the roller so the web enters vertically from below with a long span (at least one web width) and a large wrap angle (90–180 deg). In the deflection wrinkle experiment, see if the wrinkles form in the center of the roller at low, then increasing tension, then test other rollers, webs, etc. It would be helpful to have a micrometer to measure the roller deflection.

Wrinkles for Nipped Rollers

For nipped roller experiments, set up a nipped roller with adjustments for pre-nip span, wrap angle, and post-nip span and wrap angle (including a web path that simulates your production web path). Look at wrinkling as a function of nip roller design, load, uneven load, and web path geometry in or out. Consider a spreader roller as the last roller before nipping and repeat experiments.

Each of these experiment sets would show differences in wrinkling between different products. They would also show the difference in wrinkles vs. level and shape of bagginess.

Does this seem simple? I've set up and run these type of trials working with a partner company in Rochester, NY, but it is something anyone could do. I could see any one or all of these options included on a coater or slitting line. Some of the rollers would be bypasses for normal operations, but give the option to diagnose wrinkle sensitivity of different products or supplier webs.

Who needs a theory of whether a pudding recipe will taste good? The best test is to make it a few times and taste it. The proof is in the pudding.

Web handling expert Tim Walker, president of TJWalker+Assoc., has 25 years of experience in web processes, education, development, and production problem solving. Contact him at 651-686-5400; This email address is being protected from spambots. You need JavaScript enabled to view it.; www.webhandling.com.

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