Maxcess International -Fife, MAGPOWR, and Tidland present Converting Blog

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Filed under: Guiding, Spreading, Wrinkling --- Tim Walker @ 09:35 AM

Please post your questions or comments on wrinkles here.

I tend to divide wrinkles into four types, each with a characteristic shape and mechanism (see extended comments)

Continue reading"Got Wrinkles?"

Filed under: Guiding, Spreading, Wrinkling --- Tim Walker @ 09:33 AM

Please post your questions on web guiding, whether displacement (a.k.a. offset pivot guides), steering, or sidelay style.

Also, feel free to post questions on automatic guiding control systems or 'passive' guiding (like crowned rollers).

Filed under: Winding, Unwinding, Roll Defects --- Tim Walker @ 08:23 AM

Is your wound roll straight? Does the side look like a phonograph record or a neatly stacked deck of cards? Or do you use words like shifted, feathered, telescoped, dished, or offset to describe the side of your roll?

Let's talk about the top cause of lateral position error in wound rolls.

On the road to straight rolls, we divide the causes of lateral errors into four categories.
1) the web shifts prior to entering the winding roll
2) the web shifts after entering the winding roll
3) the web shifts in storage or handling
4) the web shifts upon unwinding

Write in with any area you'd like to know more about.

Filed under: Tensioning, Web Mechanics --- Tim Walker @ 08:22 AM

How much should tension vary? This is a loaded question. Do you mean average tension as displayed by your tension transducer roller? ...or do you mean the actual tension in the web at point X.

I group tension problems into five categories.

1. Tension varies over time
2. Tension is too high
3. Tension is too low
4. Tension varies through the line (machine direction)
5. Tension varies across the web's width

Tension will vary. Even in closed-loop tension control, the web tension will oscillate around the set point by some percent.

Let talk about sources of tension variation, how they create process waste, and the proven remedies.

Filed under: Winding, Unwinding, Roll Defects --- Tim Walker @ 08:20 AM

Pro: Nips and the high pressure they create are required for many web processes. The high pressure or controlled gap of two nips rollers is used for coating, extrusion, calendaring, laminating, and embossing. Shear knives are a unique form of nips. Nip rollers at winding help controlled entrained air and increase roll tightness.

Con #1: Nips can create wrinkles from either uneven feeding of the web length or steering the web into shear or tracking wrinkles.

Con #2: Nips can't be perfect. The pressure within the footprint of the nip is not uniform and will vary with on web variations (crossweb thickness, wrinkles) and roller variations (diameter, hardness, alignment, deflection).

How to avoid these problems?

Nip roller systems are quite complex, but by following a list of nip system design 'rules of thumb' (ROT), many problems can be avoided.

Throughout today's live blog, I'll try to work up a long list of these ROTs, and get your comments.

Filed under: Rollers, Traction --- Tim Walker @ 08:32 AM

In a reply post to my question on 'What's your favorite rough roller?', the following questions were brought up:

'We have issues regarding keeping rollers clean, and grooved or knurled rolls present a challenge. Any thoughts on this?'

'What are your thoughts around elastomeric surfaces (can probably get higher coef. of friction, but more difficult to control roughness, except through grooving)?'

In my experience, a shallow knurled roller, where the roller is knurled, re-ground to remove burrs and the tops of the knurled pyramids, then anodized (talking aluminum roller here), leaving a groove that is 0.010-0.020" deep and wide on a 10-20 pitch is fairly easy to clean. Lots of small grooves are better to reduce air lubrication than a few big grooves, plus shallower grooves (like from the knurling process described above) are easier to clean. (continued...)

Continue reading"More on Rough Rollers"

Filed under: Tensioning, Web Mechanics --- Tim Walker @ 02:09 PM

No matter the topic, someone will always ask "What's the most important concept?" Whew. How do you boil everything you know down to one thing?

My dad once gave me advice on business (and life). He said "Follow the money".
In web handling, my advice is "follow the strain".

For web handling, winding, and slitting, it's all about STRAIN. What changes the dimensions of a product? Webs elongate in response to relative speed changes in drive rollers. Webs stretch differential to conform to misaligned and non-cylindrical rollers. Webs are forced into small gaps of nipped rollers or knives. Webs stresses relax within wound rolls as layers shift towards the core. (Continued)

Continue reading"Key Concept #1: STRAIN"

Filed under: Rollers, Traction --- Tim Walker @ 07:03 AM

I always tell people that "My dog knows the belt equation". When he's out for a walk on his leash and wants to sniff the local news posted by a previous dog at a telephone pole, he doesn't sniff on the near side of the pole. He always walks around to the other side, wrapping his leash around the pole with about a 180 degree wrap. Why? He knows that if I want him to stop, the friction that develops between the leash and the pole will make it harder for me to pull him.

The belt equation is used every day on every converting line. This simple exponential equation says the friction force required to slide a tensioned web relative to a cylinder will be related to tension, wrap angle, and friction coefficient. (continued...)

Continue reading"Favorite Analogies #3: The Belt Equation and Dog Leashes"