If you’re a new folding machine operator, don’t let the wrinkles on a folded piece lead to wrinkles on your face! There are numerous things that can cause a sheet to wrinkle as it travels through the folder but with a little patience and thought it’s usually easy to eliminate the problem and with experience, prevent it entirely.
We can probably divide the causes of wrinkling problems into four main categories.
- Fold Roller pressure
- Folding machine setup (make ready)
- Folding machine mechanical condition
Of course it gets a little complicated when you have something from each category pitching in to cause your wrinkling problem. That’s when it’s nice to have a few years in a bindery operation under your belt!
In our experience, the majority of wrinkling problems start with incorrect fold roller pressure. Let’s use an 8-page right angle brochure or signature as an example. The best way to start troubleshooting is to look at a sheet. The folded sheet will always leave clues.
For instance, which direction are the wrinkles? Generally they run in the direction of sheet travel (perpendicular to the fold rollers). If you’re looking at the finished piece and they run in the direction shown in the diagram, (upper right) it’s likely the wrinkling is happening in the 8-page right-angle section. If they run the opposite direction, (diagram lower right) it’s probably happening somewhere in the main parallel section. (There will be exceptions to this, but we’re just speaking generally.)
Check and re-set the rollers in the appropriate section as needed. If the problem remains, continue with your detective work.
Improper setup of the folder can also contribute to wrinkling problems. After the sheet leaves the feeder and just before it enters the fold rollers, it should be perfectly flat. Anything that causes it to buckle or bow anywhere on the sheet can lead to wrinkling.
Some items that can cause this include:
- Side lay set too far from the edge of the pile or continuous stream
- Side lay skewed too much
- Wrong combination of steel and/or plastic side lay marbles
- Poor or intermittent feeding
- Poor placement of, or too few sheet smoothers
- Improper placement of transport belts (older folders)
- Machine speed too fast for the weight of stock
Once it enters the first fold plate, there are other factors. If the sheet stop inside the fold plate is not set parallel to the lead edge of the sheet, this too can cause wrinkles. Pull out wheels on the slitter shafts (accessory shafts) can cause wrinkles if they’re not gripping the sheet properly. Trimming and perforating tools can contribute to wrinkling.
Sometimes it’s no fault of the machine or the operator, but of the imposition (the arrangement of pages on the press sheet.) One clue that you have a problem with the imposition is when wrinkles appear along the head of the folded piece.
Using our 8-page example, let’s say it is printed on 80 or 100# cover stock. If you can even get it to score and fold, you’re almost certain to have wrinkling along the head. The solution in this case is of course to split it into 2 4-pagers or to run it on a thinner stock.
Another common example is a 32-page 5.5 x 8.5” signature on 50# uncoated offset. One imposition folds so there are 2 parallel folds in the first section and 2 parallel folds in the right angle section. (top of diagram at left) This way will almost certainly wrinkle at the head, since it is somewhat closed off and air will have a problem escaping. Usually a perf along the edge of the lip is needed but it still won’t eliminate the wrinkling. If you’re lucky, the wrinkles will trim off when the book is stitched.
The other imposition shown requires 3 accordion folds in the first section and 2 parallel in the right angle. In this case the air has plenty of room to escape at both the head and foot as well as along the perfed lip.
Impositions are a planning issue. The right imposition should be selected for the paper you plan to run. Sometimes you have no choice but to deal with a bad imposition. In that case, be sure your scores are very strong and accurately placed. Use a perforating blade that allows plenty of air to escape. Then play with the fold roller pressures to minimize the wrinkling.
If you’re working with older folding machines, there might be mechanical factors at play in your wrinkling problem. Worn fold rollers can cause wrinkling. I’ve seen operators running machines with chunks taken out of the fold rollers who wonder why they are having problems. No mystery there! Worn fold roller bushings or bearings are also a problem and should be replaced whenever the fold rollers are replaced. If the rollers are dirty or have excessive buildups of ink, varnish and paper dust, this too will cause problems.
Now that we’ve scared off all the novice operators with a big troubleshooting list, we’ll say this: If you’re running a relatively new folding machine, if you keep it in good shape and you learn how to operate it correctly, you’ll rarely have wrinkling problems. The new machines and their fold rollers have come a long way in eliminating wrinkling problems even at high speeds and on light stocks. But should you encounter a problem, just stop, take a look at the problem sheet and put on your detective hat.
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