We are having problems with wrinkles with an uncoated sheet, printing the 2nd side, we're getting wrinkles in the middle of the sheet, coming in from the tail towards the middle. Some are really bad and run halfway up into the sheet. One run we did had none and the next run is terrible. Coverage is very similar on both runs. Heidelberg SM72. 17.5" x 22.5" sheet. Any ideas on what to do? Thanks
Grain Short. I bring this up a lot but they tell me that for a half size press most of the papers you can get in our sizes are short grain? We never run uncoated, all coated before, now this special rush project book with 10 sigs and it's wrinkling on the second pass.
just realized that your the guy with the questions about ink sweep. You may be able to pick up a few tips here on the forum but i can assure you that your not going to learn how to print here. My best suggestion would be to open your wallet and hire a sheetfed pro to run your press. the only thing mentioned about the paper was that its uncoated. Does the sheet lay flat? Is your pressroom and warehouse area full time climate controlled? Multicolor printing requires constant temp. and humidity control in order to gain any kind of control of the process. The other issue is short grain paper. Im not saying it can't be done because obviously lots of people are doing it, but you couple short grain stock, with wavy stock, from a non controlled environment, and the issues are just compounded. Its not readily available but long grain paper in a half format sheet size can be had. You could always buy large format paper and quarter it to arrive at 4 out long grain sheets for press. For example..... buy 38x50 paper long grain and by the time you quarter it you wind up with 19x25 long grain.
Help Not looking to learn how to print, just for some help, value your thoughts. Climate controlled pressroom, 70 degrees, 44% RH. Paper has been in here for a week. Side 1's were printed and then side 2's were started 3-4 days later, paper sat uncovered by the press until ran back thru. Like I said, this uncoated thing is new to us, just trying to glean knowledge.
need to make sure sheet gets into headstops smoothly and timed correctly with minimum brush wheel pressure on the tail of the sheet and with minimum side guide spring tension. Flaps should be spread out evenly across sheet with an even light drag on all of them. You might try light suction on the vacuum holes near the headstops from the pump under the feed table. Might also try adjusting the compensator on your ranger drum. Good luck.
Sheets looking at the sheets that are set to go back thru, they are curled upwards all the way across at the gripper.
May be your damps are too high with water ? what kind of dampenning system on this press and what kind of coverage on the sheet ?
Don't know who told you that? You can get any size you want up to the capabilities of your cutter? So if you want your sheet size on the press as 17.5" x 22.5", then purchase your paper in 35" x 45" to give you long grain, if you can't get that, then specify to your supplier that you would like 17.5" x 22.5" in long grain only.
you say the sheets are curled upward? Do they show an upcurl turned over ready to feed or an upcurl as they came off the first pass? If they are already tuned over to print second side and they are upcurled severely they need to be broken to either flat or to be slightly curled down at the gripper. As mentioned before the register table flaps need to be set correctly and you might even need a little bit of suction on the gripper from the pump under the feed table.
Curl They were curled up pretty severe coming off the press on the first pass. They got them to not wrinkle on the second pass last night by cutting the packing under the blanket narrower than the sheet. Didn't get the details, just what I was told. They are also wrapping the skids now and putting the 2nd pass straight back thru instead of it sitting for a day or so between sides.
The cutting of the blanket packing smaller than the sheet is NOT a good idea. What happens is that the water film on the plate, has nowhere to go where the blanket packing has been cut, so it builds up to the point where it starts dripping onto the edges of the sheet. Next thing you know your delivery pile is stuck together from the water droplets.
My 2cents worth: NEVER run short grain. ALWAYS run felt side first pass. PLACE brush rollers as close (and gently) as possible to head stops, NOT at the tail of sheet. Robb
