Four Color Registration Drift

R

robb

Active member
We bought a used 2008 Heidi 52 6-color straight press with 30 MM impressions about 2 years ago, in lovely condition. But here is what she does to drive me nuts:
When I wash up a job that will continue in the morning, which of course is in perfect register, and I fire her up the next day, KMCY are now .08 to .12 apart from each other, like so:K
M
C
Y about a dot apart. This happens every single time...so I automatically send Y to tail .24, C to tail .16, and M .o8 to tail before I even pull sheets. This puts the colors in register enough to begin printing. Now, I have to watch carefully and check often, because as I run, the colors begin to drift apart and I must pull them back in register, about .02-.04 at each move of each color...this requires about 8-16 or more small moves to keep register. This takes about 2M-4M sheets for register to stop drifting and remain stable, and then I can relax a little. UNTIL I wash blankets-then I get to go through the whole process again because they will be out again immediately, but with this difference-within 200 sheets they will drift back together again by themselves, so sometimes I'll just waste the paper. If I wash only one blanket the drift is only 1/4 as much, 2 blankets 1/2 as much, 3 blankets 3/4 as much, so I stagger my blanket washing. Other info:

I run KMCY because 2 main customers use deep, rich blues and MC prints smoother.

The drift pattern is ALWAYS K
M
C
Y, with Y to the gripper, no matter which of the 4 colors I register to while she drifts.

This happens on all coated stocks no matter if it is 80# text or 12 pt. board. Does not happen on any weight uncoated stock (boy do I love running uncoated). Also, she drifts on the coated side of a C1S stock, but not on the uncoated side, no matter the weight of stock.

She drifts more at high speeds than low speeds, but it is always there.

After washing all blankets, the very first sheet is in register, and she slowly drifts out (in the pattern mentioned above) slowly more and more, sheet by sheet, until about sheet 50 which is the most out, and then will more slowly drift back to good register by sheet 200 or so.

I have played with packing, plates, blankets, tensioning, gripper bite, pressures etc. No change.

She has done this from day one...with only 30MM impressions, now 42MM. I don't get it. Any Ideas?

your friend and mine,
Rob
 
Try printing one color at a time or in combinations -KC, KM, KY- and check your registration from tower to tower it could be transfer grippers, also try feeding paper with no impression and do a sudden stop and try to pull the sheets from transfer drum at each tower, perhaps you might pull paper away and find the culprit, unless it is ink problem and try changing to a less tacky ink
 
I agree with Manprint, you must check your gripper settings or may be grippers need to be replaced.
 
the situation you describe is not at all unusual. Its to be expected that there is a small amount of change in fit when starting up a running job in the morning. The running condition as far as fit is concerned is influenced by many variables. Ink tack would be the first one that comes to mind. Roller temp would be another. Water feed would be all settled in too. Your press is going from a balanced condition, with stable roller temps, ink tack, emulsion stability, ect., to an entirely different set of operating conditions the next morning.
My suggestion would be to run the press with dry rollers in the morning for a little bit, to build some heat up in the inker. About 10 to 15 minutes should be long enough at about 7500 per hour. While the press is running and building heat you could get the fountain solution pumping, metering rollers set up, and fountains filled. Then ink up the rollers and let the freshly inked rollers run on high speed for another 5 minutes or so. Try this a couple of times and report back.
Even after all I've mentioned you may not start up in the morning in perfect register. You have seemed to come up with some pretty particular corrections to get it back into register. Any change at all to the amount of correction should you opt to take my advice would be a step in the right direction. These are the very type of variables that upper management refuses to consider in many cases, but after may years on the front lines of a sheetfed pressroom I've seen over and over again.
One more thing.... Is the variation as pronounced when running long grain paper???
 
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Yes, I have tried a less tacky ink, and a slower drying ink, with no change in drift.

And, I have done the E-stop test to pull and feel sheets through the press, because that is always the first thought- worn grippers. Grippers seem fine.

As Alibryan says, why is it so doggone predictable and consistent? If grippers are going bad (after only 30 MM impressions) seems I would have many problems like doubling, slurring, wrinkling, sheet- to-sheet misregistration, and who knows what else. Replacing grippers on a 6-color press is way expensive...with no guarantee it will fix problem...if drift is still there, Heidelberg will not refund my money.

What does a pressman see when grippers begin to go bad?

Thanks Manprint...aqazi81...alibryan.
 
seems like I just finished editing my post when you were posting your last post robb. Re Read my edited post to see if you got it all.
 
turbotom,

Aha! I like your thoughts...I will try as you say, because she does seem to have to get into the smooth mode, which I could replicate by doing as you suggest. And you are correct, as I am so used to it, I will notice immediately any improvement.

I only run long grain, don't know what short (wrong) grain would do.

It will take a few days but I will let you know how "pre-warming" works.

Thanks
 
Register Variation.


The problem is specific to this one Heidelberg Press, Turbotom, is just repeating "De Facto" input

parameters for every modern Four Colour Press and the many other valid comments posted.

With this large register variation, I would first check:

1) Does every press unit "Register" on its self ??

2) Check all Backlash Gearing.


Regards, Alois
 
Thanks Alois-2 questions,

1) what is meant by a press unit "Registering" on its self?

2) how does one check Backlash?

Rob
 
registering to itself would be to print a single unit or any combination of units and place the printed sheets back into the feeder for a 2nd pass to see if the selected unit or units print in register to the first pass.
The backlash alois mentions would be verified more so, if you noticed a change in register as you change press speeds. The change in press speed would have the cylinder gears meshing at different contact points.
 
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If it were a gripper/gear lash issue, there would be slurring/doubling in images. No mention of that. How clean are the images, Robb?
 
Images are clean and crisp...she prints beautifully.

Units do register fine to each other, and no register problem with speed changes, even large changes like 8M to 13M.

Turbo...the morning warm up trick does improve the morning startup perhaps 25%-50%, but of course the drift after washing blankets remains the same.

Also I should mention that, although stock thickness does not matter, ink coverage does-the more coverage the greater the drift after cleaning blankets.
 
Robb - I can't see how this could be anything but plate cylinder double gear issues, whether due to lack of lube or failure of mechanical components. You mentioned earlier something about the expense of a gripper job and no gaurantees by Heidelberg that it would remedy the "drift"...if a Heidelberg tech actually suggested the option of replacement (at only 30 - 42 million impressions!!!) or adjustment of grippers for this problem, I would be very surprised. Or, you are being taken for a ride. The double gearing must be looked into, but it's most definitely not a "do it yourself" task. Best of luck to you, Robb!
 
robb said:
Images are clean and crisp...she prints beautifully.

Units do register fine to each other, and no register problem with speed changes, even large changes like 8M to 13M.

Turbo...the morning warm up trick does improve the morning startup perhaps 25%-50%, but of course the drift after washing blankets remains the same.

Also I should mention that, although stock thickness does not matter, ink coverage does-the more coverage the greater the drift after cleaning blankets.
Click to expand...

A small change in fit is to be expected after washing blankets. This is one of the reasons I find it so important to run minimum spray powder on the first pass of a press run. Avoiding blanket washes and production interruptions whenever possible, will give you the bast chance of color and registration consistency. If at all possible, its advisable to only clean the blanket that has the defect, and to take it a step further, only clean the defected area on the blanket in question.
This is one of the best reasons I can think of ,when making a case for buying a quality sheet of paper. Its very hard for the bean counters to justify the additional cost of a quality sheet of paper. Most would rather buy the cheap stuff, and when the inevitable color and register variations occur, point the blame towards the press crew. A quality sheet of paper will in most cases avoid the frequent stops and starts associated with print defects. This state of uninterrupted running will not only make for more consistent color and registration, but also allow the press to better achieve its highest production capabilities.
 
Hey! Lighten up, Alibryan! Like the "million monkeys banging on a million typewriters will eventually produce the entire works of Shakespeare"...the more ideas on this that are thrown out there, eventually someone will hit on the answer :)
 
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