Scumming Mystery

[robbg439]

I run a Hamada 611 ECD duplicator press with a crestline dampening system, usually with electrostatic plates but also some metal plates. It has run great for me for a number of years. Over time, however, I have been having more and more scumming that occurs in a stripe that runs parallel to the paper path, always in the same exact spot (see attached image for an especially bad example). I'm wondering if anyone knows what causes this and, of course, how to fix it. So far I have checked all roller pressures, and thoroughly deglazed all rollers, added alcohol AND propylene glycol alcohol substitute to my fount. I also just replaced all my ink rollers. I'm really hoping the solution isn't to replace the crestline rollers, because they are SO DAMN EXPENSIVE. They are about 3 years old, and cosmetically very clean, and theres no swelling or deterioration on them. Any ideas?


Thanks so much.

 

[Green Printer]

After 3 years they probably are very hard and out of spec durometer. Not much choice except to change some rollers. The R,S, L, W rollers need exchanged. The T roller could wait til last.

 

[[email protected]]

I am sure that Green Printer is right. You can test by inking roller up with a tiny amount of ink than pulling thin paper carefully through rollers, if the rollers are uneven
it will show on the paper. The best way is out of press.

 

[Dan Roll]

This obviously does not represent the majority opinion, but I do not think your rollers are the issue. The rollers on this machine are not large and if one or more rollers were causing the problem it should repeat before you reach the end of the sheet. I would remove the blanket and run the press for a minute with the ink and water engaged and see if the pattern still shows on the plate. I suspect it will not, and if it doesn't, your rollers are not causing the problem.

 

[Al Ferrari]

If water rollers are not the cause of the problem, then what explains the repeat gross pattern of dark and light toning running down the length of the sheet? That pattern indicates a low spot on one of the water rollers. The Crestline system is designed to deliver a very thin film of water, so it does not take a very low spot on one of its rollers to cause the problem indicated by the pattern shown.

Al

 

[Alois Senefelder]

Press Rollers

Press Rollers

Hello fellow Lithographers,

Enlightenment - 1) all Compliant Rollers are driven by Traction NOT Gear Driven 2) we are told this "Mark" appears


exactly in the same place - this fact indicates a mechanical problem 4) measure the distance


from Grip Edge to Mark then divide the distance (mm) by 3 (pi) this will give the approx dia.


offending roller.



Regards, Alois

 

[pdan]

Elecrostatic plates are extremely sensitive...much more than silver emulsion.

3 years is old for Dampening Rollers. Original rollers from certain manufacturers can go 4 years, but someone chime in...
To my understanding, Crestline and Syntac are now merged (Parmarco?). Syntac rollers will not last five years in a dampening requirement.

But the image scan as I see it would have me taking a close look at the Electrostatic Platemaker. I've seen plenty of low spots on rollers, but they do not mainifest in this condition. I'd expect swollen roller ends causing build up at the outer edges of the plate. This is a different condition.

 

[robbg439]

The form and pan roller are gear driven. Also, if you refer to the image, when I said the mark appears in the same "place" I meant the same horizontal position on the page, in a vertical stripe that can appear anywhere on the page. Also interesting is that even in my previous set of water rollers, if anything was going wrong with the ink/water balance (ie not enough water going to plate, too much ink going to plate, wrong mix in the fountain solution) scumming would start to happen in this very same horizontal position.

 

[pdan]

Check the transport rollers in the camera - mark up a plate or press sheet. Place it near the rack or run it thru and stop. Is there a partial roller in this area?

 

[RGPW17100]

Take the crestline rollers out and scrub them with pumice or clenser. Run them in a bath of vinegar, alcohol and water and see if that improves or has no effect. If so your rollers are shot. If the electrostatic plates are the issue hang one upside down so the gripper is the tail and tail is the gripper. If it is the plate the mark should move.

Do you run the plates through and etcher before you print? If so the etcher rollers are probably dirty or shot

 

[Dan Roll]

I based my observation on the belief these marks run across the press, not from lead edge to tail, from observing the enclosed image. If this is correct, I am still dubious the rollers are at fault. All of the rollers are small enough the pattern should repeat, though it may not be as distinct, before the end of the sheet is reached. If the pattern is across the sheet, I think the plate/blanket cylinder set-up needs investigation. If the pattern is around the cylinder, I would look for a swollen spot on one of the form rollers in line with the pattern or some bunched up packing under the blanket.

 

[Al Ferrari]

Dan,

You should read the original post more carefully. The OP describes "a stripe that runs parallel to the paper path, always in the same exact spot (see attached image for an especially bad example)." That means indeed from lead edge to tail.

My observation is that the scumming in the posted image contains gear streaks and a repeating macro pattern of dark areas separated by a distance corresponding to a water form roller circumference. This can be tested by lightly inking the rubber water forms, removing them from the press, and rolling them on a large piece of paper on a table top. This will immediately show which rubber roller has the low spot.

Al

 

[Dan Roll]

Hi Al,

What the post says is clear, but I do not see a gripper margin where one ought to be if this marking is around, rather than across, the cylinder. I was only suggesting an experiment; removing the blanket, running the ink and water, and inspecting the plate for the pattern, if the problem is caused by a low spot in a dampening roller as you suggest, the pattern should still occur under those circumstances. I learned long ago not to take every bit of information literally, it is an easy way to be mislead.

 

[Al Ferrari]

Dan,

Take another closer look at the OP's jpg. Note that the scumming bleeds at the bottom of the image, but not at the top because that is the gripper. Your skepticism of the descriptions in posts is healthy up to a point. But your not believing the OP's statement that the scumming runs in the direction of the paper travel goes overboard.

Please comment instead on my observation that the distance between the dark scumming areas represent a dampening roller circumference.

Al

 

[Dan Roll]

OK Al,

If the scum pattern represents a roller circumference (or two roller circumferences) going around the cylinder. I would look to the bushing or bearing for that roller on the affected side of the press rather than for imperfections on the roller surfaces. It looks to me more like something is dragging on the plate surface. A low spot on any of the dampener rollers other than the form roller would transfer more, not less, water and the printer in this case testifies the rollers look to be in good condition. The Crestline Dampener we used to print our labels functioned flawlessly for well over a decade without replacing a single roller.

 

[Al Ferrari]

Dan,

Your "something is dragging on the plate surface" comment has merit. Especially in connection with the comment by

robbg439 at 01-24-2014, 01:26 PM:

"Also interesting is that even in my previous set of water rollers, if anything was going wrong with the ink/water balance (i.e., not enough water going to plate, too much ink going to plate, wrong mix in the fountain solution) scumming would start to happen in this very same horizontal position."

Clearly we need for him to return to this discussion.

Al

 

[jaed]

I've seen issues like this when ink tracks back onto the chrome or metering roller on a two chrome water system. The idea is that ink, being hydrophobic, that builds up in the water rollers stops the water from transfering properly. My suggestion would be when you get this problem completely remove all ink from all of the rollers in your water system with out touching the ink train, and once the water system is completely clean try starting up again and see if you are still having the problem.

 

[Al Ferrari]

Thank you for participating jaed, but we are not dealing with a standard water system. I suggest you read up on metered dampening in general and Crestline dampening in particular.

Regards,

Al

 

[Dan Roll]

Just to clarify for those unacquainted with the Crestline dampener, the dampening rollers are supposed to ink up just like the ink rollers and this allows an even distribution of the fountain solution to the plate. It is not often one hears of problems running a Crestline, there are a lot of them out there and for the most part run really well. There are two versions, a four roller and a five roller. I only have direct experience with the five roller system and never had any trouble with it at all. I believe the dampener on the press this thread is focused on is a four roller system, but the principle is the same as the five roller design.

 

[robbg439]

Sorry for the long absence, but here's an update. I caved and bought a new set of crestline rollers, which of course were backordered, hence the long silence. Anyway, the did the trick. I forgot how nicely my press could print. These fresh rollers are putting a lot more water on the plate, so I do think that the rollers I was using were hardened. Dan, it seems like from your comments that there might be something going on in the crestline that might make my rollers degrade faster than they would otherwise. I inspected everything when I took the press apart to install the rollers, and didn't notice anything out of the ordinary. But I will keep an eye out.

Thanks everyone for your help. I love this forum.