7 o'clock & 5 o' clock cylinder alignment

OSS

Well-known member
Want to know the difference / advantage between 7 o'clock & 5 o' clock cylinder alignment in detail

Regards
OSS
 

robb

Active member
The 7o'clock config is the better choice because the sheet is completely printed before the following sheet enters the nip. This is important because, in the 5o'clock position, you can (will) get a noticeable streak on each sheet, which comes from the sheet following it entering the nip and shocking the unit the tiniest bit. Mostly it is not noticed until you are trying to run a clean beautiful screen. This is sometimes known as a "bump shock". I solved the problem by "feathering" the lead edge of the blanket packing on all units-this smooths out the 'bump' at the nip.
 

Alois Senefelder

Well-known member
Hello robb,

The problem you have and describe is not related to the 5'o'clock/7'o'clock cylinder configurations. What you are

seeing "Cylinder Gap Shock" - WHICH is the result of incorrect Pre-load Tension.

Signs for this problem: 1) are the plate cylinder bearers clean and bright looking around

the cylinder circumference - Yes/No? 2) Is there a visual streak mark on the bearers at the lead /grip edge

of the plate cylinder - Yes/No?

The Cure: the cylinder pre-load needs resetting by the press manufacturer engineer.

Regards, Alois
Cyl Gap Shock # 1085.jpg
 

robb

Active member
#1-yes #2-no

Mr. Senefelder,
I respectfully beg to differ-what you refer to can produce a streak, but not the streak I am seeing.
Heidelberg press operators and mechanics refer to it as the "Heidelberg Bump", although a more accurate name would be "5o'clock Bump". Old or new, any press, even in perfect condition, at 5o'clock config, will produce a streak-this is why most sheetfeds are designed at 7o'clock. A two color Heidelberg S press is configged this way-
1st unit-6o'clock and 2nd unit-5o'clock. A fine overall screen will have a 'bump streak' if run on unit 2, and will not have the streak if run on 1st unit. I was pleasantly surprised that the 6o'clock config was enough to eliminate streak.

My experience as a pressman tells me this is true: an actual condition I have seen over and over. I also respect your judgement-what do you think?

Just for the fun of it, I'll mention another streak provider that comes at higher speeds when the ink ductor smashes full against the roller train. This has, of course, been designed out of the ductor by letting one end hit first.
 

robb

Active member
Good thoughts, good descriptions.
I would like to go a little further now about CGS from your PDF report:

#1-Why is it important to ensure that the sheet is fully printed before transfer? Is it because a shock streak can appear if the sheet is not fully printed even with correct pre-tension of bearers?
#2-Nice description of the bearer's job.
#3- Ductor streak-Perhaps "smash" is a little strong. Here's my experience. Most ductors duct on every other revolution of the press. I trust that it ducts in the gap, certainly seems sensible. But I get a streak (in fine screens, caused by the dots doubling the tiniest bit, about an eighth to a quarter inch wide, and across the full width of the sheet, which is visible on the blanket also, in exactly the same spot on all units). And the faster I run the press, the more noticeable the streak. I finally realized that the streak on every other sheet is slightly lighter (paler) than the sheet before or after it, as if the blanket is trying to clean itself up for one revolution. Then I realize the ductor swings every other rev. So I shut off the ductor, and voila! no streak. A Heidelberg mechanic/repairman comes in on another problem, I give him my thoughts on the ductor, show him what I have found. So he checks the bearers, pre-load, blankets, packings, and other things I know nothing about. He is stuck, so he calls in to Heidelberg, and after a long discussion, suggests that we remove the gear that is driving the roller that the ductor hits-so it is not in the gear train and is essentially a rider roller now. Again, voila!, no streak. Problem solved. In my spare time I took the gear out of all units.

Thanks for listening. What do you think?
 

robb

Active member
Mr. Senefelder,
A picture is worth a thousand words-I see and agree, why would you transfer sheet before it is fully printed. Only makes sense.

About the ductor problem, yes, all roller settings were checked and set, many times. Your question about Why Me on my press, I've been asking myself for years. I have wondered if it has to do with the fact that the press is a 5-color MO, that is, a Heidelberg MOVPP, 5 0'clock arrangement. I believe the MO is kind of a weak Mom and Pop shop kind of press, true?

I cannot post picture, I've been retired a few years, annd the press has gone to Mexico.

Thanks for the education-always a pleasure.
 

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