Trouble feeding curled paper when backing up sheets

[jotterpinky]

We are running a Ryobi 524 that we just purchased. We're having quite a bit of trouble backing up sheets with any sort of coverage. The paper is just too curled to run back through the feeder.

This is what we've tried
1. running minimum amount of water - to the point of just above scumming
2. not running the IR dryer which we think might increase the curl
3. de-Curling the paper BY HAND (not too fun on 200,000 sheets)

This seems to be a big problem on lighter weight stock. We just ran some 70# coated and the density of the image on the front was such that it was curled beyond running without manually forming the paper.

From what I've read we want to make sure the grain direction is parallel to the gripper but that seems counter-intuitive for curling.

Any thoughts on how we can get around this issue or some things other people have tried? Maybe we're the only ones who have this problem?

 

[RGPW17100]

This is quite common with lighter weight coated and matte stocks. Our SM52 has a sheet decurler but that seldom fixes the problem. Only thing I can think to help is always run the curl up side first on text weights. If you run curl down first you will amplify the problem. For this reason we will not run less then 80 lb gloss and if we do it is a lot more expensive even though the stock is cheaper. We spend quite a bit of time hand decurling on back ups. Try and see if you can get the customer to let you use a heavier sheet. I assume the 524 does not have a coater. This might be a problem as well with the extra powder you need to use to prevent sett off.

 

[jotterpinky]

No it does not have a coater...does a coater alleviate the curling problem to some degree?

Have you found the paper grain makes much difference?

 

[HPC]

We run smaller sheet sizes but the concept is the same. My folder loves up curl, so what I do is put furniture (wood sticks) at the front of the sheet to make it curl up. One other machine will run only flat stuff, so we use chip board approx 1/2 by 1/2 in the body of the stack to make it flat, no hand work. All depends on how your press feeds and what it likes. Hope this helps.

 

[DotBox]

some other options

some other options

If you've NOT been having drying problems lately, you can try reformulating your fountain solution mix and running even less water on the press. Typically, adding more concentrate to the mix will slightly increase the tendency to scum but reduce drying time, so you may want to go the opposite way: remove some of the concentrate from the mix, thereby increasing drying time but reducing the chance of scumming. Then, you can back off on the water settings even more than you currently have, and if that reduces the curl enough you could possibly turn the IR dryer back on, too. Just make sure you don't reduce the acidity too much or it can take a much longer time for the sheets to dry. (I realize most all concentrates are now pH buffered, but the overall concept can still work, just in a narrower range than in the "good old days".)

Curl is often amplified by shop environmental conditions as well. If you haven't already done so, acclimating the stock within the pressroom area for a longer period of time before the run will sometimes help prevent curl from happening later on.

I don't know if this has a better technical name or not, but when I suspect curl is going to be a problem on the second pass, I use wedges to "train" the printed stack in the delivery starting from the very first sheet. This sometimes works amazingly well, other times, not so much. The idea is to force the stack to curl (or decurl) in the direction you want, and to leave the wedges in for awhile afterwards, until some drying has occurred...maybe an hour or so. Arranging the wedges correctly can be a minor pain-in-the-rear, but when it works at all, it usually works great.

Good luck.

 

[Kaoticor]

A few things you can try on that lightweight troublesome stuff.

1: Use wedges on the first pass (like dotbox mentioned). Make sure to run curl side up first or it will be a long second pass through...

2: Run smaller stacks

3: When you restack the sheets, you can either order or custom make a base that has a hump in it. This can flatten out a really curled stack if you are dealing with curling up. For down curl, just some wedges will usually do the trick.

4: You mentioned that the run is 200,000. Are your sheets sitting a while waiting to be printed on the second pass?

5. This is a really ghetto method: If you have any old hold down fingers, (the paper guides leading in to the register stops that holds the paper down against the feeder table), you can tape them to the feeder head assembly to hold the paper stack more firmly against the stops. This will let you have a more stable pile if the stack is curled. Sounds crazy but was a trick I saw an old school feeder operator do to make it work!

 

[Alois Senefelder]

Lightweight Paper

Lightweight Paper

Hello fellow Lithographers,


In future when printing on Lightweight Paper ......................

A Pdf - I hope you will find of interest and value.



Regards, Alois

 

[jotterpinky]

these all look like good ideas to experiment with. We'll try them out on our next run of lightweight stock.

Out of curiosity RGPW17100, you mention that your 'decurler' on press does not seem to work well. I'm thinking about the possibility of adding one to our press (I believe it's an option). In your opinion is this worth the additional expense?

 

[acacia print]

One thing that sometimes helps but only a little, or seamed to help was reducing the ink tack. It is most obvious on solids that this will help by placing less stress on the paper, so I am assuming that it might help swing the odds in your favour when printing what ever you are printing... Just a thought. However if you reduce it too much then you will get other problems... I normally reduce it until the ink slides off the knife fairly smoothly, if it runs of the knife you have gone way too far.. you would then need to check in some more ink, of corn flower will work... odd but it re stiffens the ink. You can only push that trick so far though too...helps with scumming issues too..

 

[SHELBY]

70???? your having problems running?? try 50 or 60, 70 is a godsend! Flip your stock before you load it.Decurl it and run the damn thing!If you cant get 70 to feed and I dont care about the coverage you need a new trade! I wont get into running onion skin.

 

[HPC]

[ I wont get into running onion skin.[/QUOTE]



Wanna try Mirra form 10.5#?? That stuff was sooo much fun.

 

[SHELBY]

[ I wont get into running onion skin.

Wanna try Mirra form 10.5#?? That stuff was sooo much fun.[/QUOTE]

I dont know what I have not tried , ncr on a 40 inch.........you name it, then I see 70 and oh the curl !200,000 sheet to decurl is a cake walk in my books. try 2.5 mill run on 50pound loaded with a varnish to boot on a 28x40.Month after month........year after year.
This trade is going down hill, and fast.

 

[Kaoticor]

Alois,

Do you have any experience running double suction cups? If so, have you noticed any significant benefits to running them??

 

[jotterpinky]

Shelby, since you're running such light stock how do you deal with the curl effectively, I'm assuming you're not manually decurling such large runs. Any thoughts for the rest of us?

 

[Tashi D]

De-curler works great on first pass but be advised its deseign is to induce an upcurl in each sheet by applying a vacuum between two polished cylindars. It can sometimes scratch the back of cheap coated stocks and if your pressman forgets to turn it off for the backup it will destroy all your fine work