Thread: Doubling problem

Hello everyone,

I'm operating a 4 color CD102 and lately i've been experiencing doubling problems in the first unit which is usually black. It seems like i have a problem with the 2 set of grippers on the impression cylinder in the unit (that's what i thought at first) but we called a guy from heidelberg only to figure out that the grippers are adjusted correctly, the cam followers are just fine and the opening/closing times are optimal. He also checked the first transfer triangle(3 set of grippers), front lays, plus the transfer gripper from the front lays to the impression cylinder with the same results. He couldn't figure out whats wrong, so in the end he suggested i need new set of grippers on the impression cylinder, telling me he wasn't sure about it but he had to start somehow in order to figure out whats wrong.
Now, the machine has like 70 million impressions and we rarely use heavy stock. Personally i don't think i need to change the grippers but it seems i have no other choice. I have this problem for a couple of weeks or so and i need to find a solution soon.
When i print the typical four color job, i can see how black is moving up and down as it goes through the other units, but not evenly. I can't tell if the problem is in every other sheet or every 2 sheets.
It seems the problem is viewable from the middle of the sheet(70x100) to the top no matter what stock i use. As it goes from the middle to the top is getting worse, but from the front lays to the middle is barely noticeable.

Any Suggestions?!

KostasK

Kali mera

Did he or you check the sheet compensator?

You might have a hard time finding a sheet compensator on your CD102, some of the things I would check is first make sure the sheet is going into the press ok. Make sure board register is good. Try printing only the first unit and print those sheets again. Idealy you want to see no double image throughout the sheet. Also the type of paper you are using could also make it look like there is a double. Typically the thinner, uncoated, cheaper quality paper will show a double. Also I think it goes without saying that paper is long grain. Next I would check your blankets. Make sure your blankets are high quality blankets. Day 3000 are probably the best blankets to use on that press. Blankets should be packed correctly as well, WITH A PACKING GAUGE. Blankets should be packed at bearer height or slightly under once worn in. Make sure blankets are torqued as well. Blankets on the press should be torqued to 56 foot pounds. I dont know what that is in NM. Another thing to check is the urithan on the grippers. Many CDs came out with urithane grippers. It is not uncommon for the urithan to come off around 70M impressions, however unlikely. Usually if grippers are begining to fail on one printing unit, you will see it on all. Just like tires on your car wear somewhat even, so do grippers. And, just like tires, you dont just replace 1. If you are going to replace grippers you need to replace all units...with steel grippers not urithan.

Originally Posted by exheidmech

You might have a hard time finding a sheet compensator on your CD102.

If you lift up the feedboard you will find the sheet compensator in the center next to the front eye adjuster, it will be marked (from memory) +4 to -3 ....i think !! This device actually bows the front lays which can make a big difference to the sheet on the first unit.

Regards.

Hate to tell you this, but thats not a sheet compensator. Sheet compensator is found on older presses, not likely to see on a CD. if your press has a ranger drum, (register feed drum) it has a sheet compensator. I cannot recall any CD having a ranger drum. They may be out there but I dont recall ever seeing one. Presses with a swing gripper and a transfer drum do not. What you are thinking if is a way of "bowing" the head stops, again not a sheet compensator. This bowing of the head stops will not likely cause a doubling.

Originally Posted by mrheidelberg

If you lift up the feedboard you will find the sheet compensator in the center next to the front eye adjuster, it will be marked (from memory) +4 to -3 ....i think !! This device actually bows the front lays which can make a big difference to the sheet on the first unit.

Regards.

Ahem, well all the engineers I have spoken too called it a sheet compensator and that was on a CD and CP200, still seeing as you're an Ex Heid Mech, you would know best

Thank you all for the immediate responce

I use zaphira blankets and never had a problem, but in order to be sure i'll get those day3000. If the sheet compensator is the device under the feedboard that bows the front lays, was one of the first things i checked.
I tryed to print the first unit only and then pass those sheets again. I could see clearly that the black(first unit color) is moving up and down half milimeter but not evenly. Sometimes is every other sheet, or every 2 sheets or even three.

I called a freelance engineur to visit on monday see if he has a better idea

Exheidmech: I totally agree, its not normal to get problems with the grippers on one unit only plus i didn't have this problem at all two weeks ago. I don't think is common to get these problems from one day to another, thats why i don't think i need to change the grippers. At the time i switched black with yellow and its barely noticeable

I'm thinking maybe somethings wrong with the feedboard and the frequency the sheet is approaching the front lays, but on the other hand thats something the sensor would have beeped at.

I think the fact that you are seeing a double image when printing PU 1 twice showes there is an issue at the infeed. Could be grippers on the transfer cylinder or even a possible bad cam follower on the swing gripper. Bear in mind there are 2 cam followers on the swing gripper. Also see if the issue shows on both side guides. Could also have a problem at the side guide. As far as the press beeping with the sheet going into the press, that is only if the sheet is not pulling, or pulling too far into the side guide. The press will not beep if your sheets are bouncing at the front lays.

Originally Posted by exheidmech

Bear in mind there are 2 cam followers on the swing gripper.

Are you sure about that? I'm pretty sure there is only one cam follower on the swing gripper. Is there a chance you mean the cam follower on the front lays?

There are 2 cam followers on the swing gripper, one of operator side, one on drive side.