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.

 

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.

 

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.

 

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.

 

Probably you have a problem on the axle grippers. The bearings of the axle suports are damaged, so the axle is damaged, too. Try to have a look at this
Sorry for my bad english :$

 

What are axle grippers?

 

Kostas Kapa

I have seen this sort of thing happen to one of my presses. Heidelberg was here for a couple of days and replaced everything under the sun (ie: infeed grippers pinsor gripper ect.). Turned out the Press became un-level somehow between PU#1 and PU2.Once they leveled the press it went away Instantly.

 

I'm just about to replace the grippers and pads(under the grippers) on the first impression(2 set of grippers) and the trommel cylinder(one set) hopping that the problem will go away BUT the thing is that my machine became also un-even somehow especialy between units 1 and 2(mechanic checked that also in order to figure out whats wrong). I asked the mechanic if this is causing all of these but he assure me its not. Well i'm not sure anymore.

How difficult is to level a press once its already installed?

 

As long as everything from unit 2 onwards is fine it should be relativley easy to split unit 1 and then re-level unit 1 and the feeder.

 

I wouldnt think it has anything to do with the level of the machine. Although it is possible, it is unlikely. How long has the machine been sitting on the existing floor? If its been more than a year or so, its not likely the machine is out of level. There are ALOT of machines out there that have been installed by unqualified mechanics that are running ok. I would pay more attention to the infeed, head stops, side guides, grippers, cam followers, thrust bearings, blankets, I would also check to see the belt on main motor in good shape and tentioned correctly and maybe as a last resort check level. I forget what your original post said, is your movement front to back, side to side or diagonal? front of sheet, back of sheet or overall? If it does get down to releveling the machine, it is not as easy as one would think. Drive side and operator side catwalks have to come down, oil needs to be drained, periferal equipment on drive side needs to be moved, intermediate guards on drive side and operator side need to be removed, bolts need to be loosened and then you can relevel. Resealing the press sometimes can be a chore, and then of course releveling the feeder. Depending on how far it would need to be releved it could take up to 3 days and sometimes more.

 

exheidmech

The movement on the first unit is clearly up and down(circa half millimeter) and its more intense from the middle of the sheet(70x100cm) to the back especially on the edges no matter what stock i use. From what i can tell, the problem is on one out of three sheets(first bad, second better, third good)

So far i've changed the blankets, cam followers on the first impression, first triangle, swing gripper and trommel cylinder, checked side lays, front lays, grippers+opening and closing times. Last week had a printer from heidelberg to confirm i have no problem with the feed board and right now i'm totally out of ideas. Machine its been on the existing floor for 3 years or so.
One important thing i forgot to mention before.. When i got this problem for the first time, something else happened at the exact same time: The bar of the Autoplate of the same unit, kind of changed its position and lost completely my register. I had to fix it manually later on and bring it at the correct position again. The strange thing is that both problems happened without warnings or signs and from one moment to another. I had the typical four color job, passing sheets to reach the density, eventually i did, customer said ok, while sheets were waiting on the feed board i pressed the green button to print the job and thats when both problems began. The Register part was easy to fix, the doubling still giving me the headaches and i'm kind of tired printing yellow first unit.
At first i was sure both problems are connected somehow, but i had three different mechanics over here and couldn't find the slightest connection.
Auto register motor was checked with no problems at all, and plate cylinder is definitely not moving as the picture and letters comes sharp on the blanket.

Assuming all of these i'm really starting to believe that both problems are somehow connected with the fact the machine became unleveled somehow especially the first unit compared to the second. Well ok except for the fact that machine doesn't lose its level from one moment to another. I guess i should be getting signs or something even though i'm located in Greece and small earthquakes happen often.

So far the only option the mechanics has given me, is change both bars and grippers(2 set complete) on the impression cylinder, but i don't think this will solve anything.

 

If you have only front to back movement it can only be a couple things assuming your infeed is ok. Grippers and cam followers. I would make sure all grippers and pads are clean. Make sure all grippers are free and not frozen on shaft. I would double check to make sure all cam followers are ok, 2 on impression and 3 on transfer. Make sure cam followers are ok on swing gripper keeping in mind there are 2 cam followers on swing gripper, one on operator side and one on drive side. Where is the main motor located on this machine? If it is located near the first or second unit you may want to check condition of drive belt and make sure it is tight enough. Have you had any infeed crashes on the press? When you print only the first unit does the press have good board register? It is also possible that a impression cylinder gear or tripple drum gear have been bumped out of position if there was a crash. This is not an easy repair and I wont go into what is involved in this repair, hopefully this is not your problem. I would guess drive belt or something has been over looked on infeed.

 

Check the impression piston. The lock nuts sometimes work loose and the piston (threaded connector) works loose. I've seen it look like a slur or doubling.

 

kosta the mech is right . 2 cam followers. But mech, i believe that if there was an infeed problem, he would have register problems on all colors. Kosta, i can drop by and check your problem. Just send me a mesage and we can arrange something. You did check the plate clamps didnt you?