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

« Home » November 2006

Filed under: Guiding, Spreading, Wrinkling --- Tim Walker @ 08:00 AM

Contributed by Tim Walker -

Question:
When plotting a film's shear wrinkle sensitivity vs. tension or strain, thinner films wrinkle easier for the same tension, but thicker webs wrinkle easier for the same strain. Explain this.

Also, what is the effect of crossweb thickness variations on wrinkle sensitivity?

Thinner web will have fewer wrinkles if you compare two webs at the same tension (tension defined in force per width). For a given tension, a thinner web will have more tensile stress and more strain. This may add enough tension stiffening effect to make a thinner web stiffer.

I don't think that small web thickness variations will create more wrinkles. Thickness variations at winding will create wound roll stress variations that often lead to making baggy web and baggy web will have more wrinkles, so indirectly, thickness variations may promote more wrinkles.

Filed under: General Business Topics --- khevenor @ 01:35 PM

Just a few weeks ago, I wrote about the importance of maintaining safety and having comprehensive disaster plans in the workplace. You can read that post here. Right before Thanksgiving, those of us in the Boston area had a startling example of just how important that is. CAI, a manufacturer of inks and coatings for applications such as flexible packaging and paperboard containers, suffered a massive explosion in its Danvers facility just before dawn on November 22. Fortunately, no one was killed or seriously injured, which is amazing to those of us who have seen the footage and photos of the damage. The Boston Globe article describes in detail the blast that blew people out of bed, shattered windows, destroyed cars, and rendered homes uninhabitable.
Exactly what caused the explosion has yet to be determined. But from all indications, CAI had an impeccable safety record and had always been respected in the community. Perhaps this is a sign that no matter how hard we try to prevent accidents, they do happen. Picking up the pieces after the accident is a challenge, and I'll be anxious to see how CAI does in that respect. This may be a good time to review your own plans ...
- Keith Hevenor
Editorial/Conference Director
CMM International

Filed under: Slitting, Cutting --- Tim Walker @ 08:00 AM

Contributed by Tim Walker -

Question:
Can shear slitting scratch a film web? Is there any relationship between slit and web speed?

The only shear slitting has problems with slitting-related scratches. The scratch is usually near the slit edge, created by the web traveling under or over the top or bottom knife in the overlap region. Too much overspeed will make these scratches worse. I don’t believe that line speed if important. Usually these scratches are eliminated by changing the knife geometry. I have heard of many shear slitting processes change the both shear knives, especially the top knife, to a wider design to avoid scratching.

Filed under: Rollers, Traction --- Tim Walker @ 08:00 AM

Contributed by Tim Walker -

Q: I have tried to add a nip roller to my process, but used a nip roller narrower than the fixed roller and also narrower than the web. The result is WRINKLES. Should I use a nip roller wider than the web?

A: Yes! Unless you have a thick and stiff web, nip rollers should always be wider than the web. Usually the two nip rollers are the same width and wider than the web. In some limited cases, you might be able to have a nipping roller just less than the web width, but I wouldn't leave more than 0.25-0.5 inches unnipped on either edge.

Why is a partial nip a problem? Nips will tend to speed up the web underneath them. If you speed up one section, say the middle, but not the edge, the result will be a severe localized speed variations that induces shear stress into the web. If the web is thin, it will wrinkle in response to this shearing.

Filed under: General Business Topics --- khevenor @ 07:31 PM

It's not like we work in a particularly glamorous business. Converting and packaging is certainly a critical element in today's culture, but not one that is typically an object of much mainstream attention. So you can imagine my surprise the other evening when I was flipping through the channels on the TV and stumbled across some very familiar subject matter on the National Geographic Channel. The program was called "Shrink-Wrapped and Boxed Up," and is described this way by the channel:

Packages have been a cornerstone of consumer culture ever since the ancient Greeks and Romans stated storing wine in ceramic vases. Shrink-Wrapped & Boxed Up takes viewer to the cutting edge of modern industry where researchers and scientistsare developing packages that can withstand the impact of an F16 airplane, outwit shoplifters and reduce the amount of landfill trash.

It's by no means a technical program, but one worth catching if and when it comes back on the air. I have to assume that like most cable channels, the National Geographic Channel cycles its programs several times during the month. Watch for it on your local cable system, and when you do see it, call your friends and family and enjoy your moment in the spotlight!
- Keith Hevenor
Editorial/Conference Director
CMM International

Filed under: Winding, Unwinding, Roll Defects --- Tim Walker @ 08:00 AM

Q1: How can you minimize web sagging in a horizontal roller?
Q2: How can you eliminate sagging rolls?

A1: If the web is sagging in a web span between rollers, higher tension will reduce web sagging or shortening the web span by adding a roller. You can offset span sag with air nozzles also.

A2: A sagging roll was usually not initially that way. A sagging roll indicate either the web is getting longer over time (not very common) or the roll’s layers are getting thinner over time. Why would a layer get thinner? If the wound roll layer include air, then the air can bleed out over time and create roll looseness or sag. If the web has a thick coating, the coated layer may with ooze laterally (like an adhesive layer), or increase it’s density and get thinner, both loosening the roll and causing roll sag. Rolls don’t automatically get loose with a small amount of web thinning. Only after the thinning exceeds the strain of the roll’s layers will they loose all their tension and sag. Winding tighter will help, but only so much.

Filed under: General Business Topics --- khevenor @ 08:32 AM

A recent story in the Packaging Digest e-newsletter reported that "A major generic drugmaker Thursday recalled 11 million bottles of its store-brand acetaminophen after it found the pain pills might contain metal fragments." Now I don't know about you, but the thought of choking on a metal fragment when I'm trying to relieve a headache just isn't appealing. Fortunately the company found the problem and is taking steps to remedy the situation and prevent any further potential risk. If it hadn't been for the quality control system and steps put in place to detect these kinds of problems, something much worse could have happened to unsuspecting consumers.
According to the original story on the CNNMoney website, "The Michigan-based Perrigo Co. said it noticed a problem when the equipment making the tablets was wearing down sooner than expected. Its quality control system detected traces of metal pieces in a small number of the caplets, it said."
Converting, package printing, and packaging are manufacturing processes, and as such are always at risk for these kinds of problems. As consumers in a highly regulated market such as the United States, we have a kind of blind faith that what we buy on the store shelves is safe for us. But as manufacturers of products or packages, it is our responsibility to monitor quality and ensure that all safety precautions are taken and all regulatory guidelines are followed.
The FDA says the metal pieces found so far range in size from a microdot to a wire fragment 8mm in length, which is certainly not insignificant. If you are providing converting or packaging services, be sure that your machine operators and quality control inspectors are current in their training and be sure that you have created an environment that encourages employees to speak up if they suspect there is a problem.
Are there other ways that you maintain safety and quality?
- Keith Hevenor
Editorial/Conference Director
CMM International

Filed under: Winding, Unwinding, Roll Defects --- Tim Walker @ 01:51 PM

Contributed by Tim Walker -

First rule of roll edge misalignment: Figure out if the web is shifting before it gets to the winding roll or if it enters the roll in the correct position and shifts later.

Q1: What causes one edge of a roll to be misaligned (but not the other edge)?
Q2: What causes roll edge misalignment only near core?
Q3: What causes misaligned roll edges as diameter increases?
Q4: What causes misaligned roll edges as speed increases?

A1: Anytime one side is aligned and the other side is not, it indicates the web width or tension is varying. When winding after slitting and one side if good, but one side is uneven, the top suspect is the slitting process. The web may be loose at the cutter causing the edge cut position to wander and width to vary or the slitting blade or knife assembly is wobbling.
If the winding alignment is controlled by a web guide, then one edge should always be well-aligned, but the other edge may wander due to width changes, tension and necking changes, or web wrinkling in the wound roll.

A2: I saw this recently on a differential winding shaft after slitting. This slitter used one of the newer differential winding shafts that have core stops to hold the core’s lateral position. However, due to core debris generation on these stops, the operators had moved them out a little, but this gave the core freedom to shift. At startup, the core shifted to one side over the first 100 feet of winding, causing a shifting of layers near the core. If you have severe shifting near the core, you likely have cinching (MD slippage) and telescoping.

A3: If you don’t use a winding nip (aka pack roller, lay-on roller, contact roller), then you may have slippage when the entrained air is greater than the product roughness. The lubricating air layer increases with roll diameter, so as some point, the air layer is too thick and the layers begin to shift.

A4: The same answer as #3, but now speed causes the increase in entrained air and lubrication.