mechanical ghosting

[Al Ferrari]

Well, we seldom bother (at least I don't) to mention that the plate and blanket cylinders are geared either, but I supposed it is a good clarification.

Al

 

[Al Ferrari]

I just noticed that Paul Cavanaugh is directly connected to Heidelberg. I wonder if he has an equally unbiased evaluation of the Anicolor press?

Al Ferrari

 

[Al Ferrari]

Yes, much better.

 

[vik la luna]

I take it by your not answering the first two questions that your not a pressman Erik, which is fine, but please don't insult my intelligence by stating your opinion when I know it to be fact.

In regards to your "not so good as to produce predictable performance", Heidelberg is the top printing press manufacturer, always have been, probably always will be. Heidelberg's engineers are like most engineers IMO, all theory, no practical experience..

Tim

wow
heidelberg is a good product but not the "top"
there is no such press, especially the much over rated heidis
also your comment is a contradiction in terms "heidis engineers are all theory but no experience" yet according to you its the best in the world!
a good pressman can make any press be "top'

 

[vik la luna]

Maybe they would be so big and heavy for say a 50" wide printing press, wouldnt the dampener have to be the same size also?

agree
imagine changing a roller that big!

 

[GazKL440]

agree
imagine changing a roller that big!

Lol i have done 2 decks in the 40" i run in the lst few weeks, and they were a bastard of a job!!

1 big cylinder sized roller...methinks you would require a gantry

 

[TheProcessIStheproduct]

Not only hard to change but EXPENSIVE...

Not only hard to change but EXPENSIVE...

On the Karat, don't think in terms of a traditional roller, the single diameter form is a blanket cylinder, every revolution it is fully charged with ink from a high line screen anilox, when you scratch one of those you are looking at $15K for a new roller and a service call (it is plumbed and you need special tools so you cannot change by your self). Bottom line on some very rare press forms you get less or even no ghosting, however, just like everything the advantage of no ghosting is balanced out by, heavy gear marks, a bounce when the blanket gap comes around (this is why some webs have gone to blanket sleeves so they don't have gaps) and specific to Karat (not Anicolor) you have very narrow op temps that have to be kept on anilox and plate cylinder as well as proprietary Presstek plates. All and all my convention press runs circles around our Karat....

 

[rich apollo]

I was thinking of a more conventional offset press - just with full-sized forms. Wouldn't some oscillators even out the ink distribution? Why is an anilox roller used in the pan on these devices? Why not a normal ductor roller?

By adding more rollers into the train, do you introduce too much ink into the ink train - more than can be pulled out?

 

[The Heidelberg Guy]

I was thinking of a more conventional offset press - just with full-sized forms. Wouldn't some oscillators even out the ink distribution? Why is an anilox roller used in the pan on these devices? Why not a normal ductor roller?

By adding more rollers into the train, do you introduce too much ink into the ink train - more than can be pulled out?

I added a picture to show more of how the Anicolor works.

 

[Deleted member 16349]

I was thinking of a more conventional offset press - just with full-sized forms. Wouldn't some oscillators even out the ink distribution? Why is an anilox roller used in the pan on these devices? Why not a normal ductor roller?

By adding more rollers into the train, do you introduce too much ink into the ink train - more than can be pulled out?

Rich,

You are asking a lot of questions in a few lines and the answers are complicated. I will try to explain what I can.

First let me discuss ink distribution in the roller train. I am talking about the ink films on different rollers. The ink films vary vertically up and down the ink train and they vary horizontally across the ink train. This is due to differences in the ink required for the image being printed, basically the coverage and due to the geometry of the roller train configuration. Many people assume that the ink film at the form rollers is uniform for high and low coverage but this is also not true and depends on roller train configuration. This is too difficult to describe why this is but when one does calculations it shows this difference. Calculations are also only educated guesses and can not model every influence but it gives an idea.

Mechanical ghosting patterns are generated at the plate and form roller region. Ink comes off the form roller and goes to the plate. This can be in patterns that do not completely get smoothed out during one revolution of the form roller. Multiple form rollers help to even out that ink film on the plate but this is not always successful. Adding ghosting rollers to the last form roller helps because it gives an extra hit to help smooth the ink film on that roller. This action of a roller smoothing out the ink film on another roller, I call random averaging because it picks up thick ink films and deposits ink into thin ink films on the form roller.

Oscillating (vibratory) rollers in contact with the form rollers provide some help with moving ink laterally to reduce ink starved areas. The problem with oscillating rollers is that their capacity to move ink laterally is very low. You can see this is you do a simple test on press. Put some extra ink in one specific location about a 1/2" wide. Run the roller train and carefully look at the thicker ink film. You can see it because it splits with a very rough ink film. The oscillating roller might move laterally almost 2 inches but if you look carefully the thick region of ink does not follow the oscillating roller but tends to move only slightly in one location. The reason for this is that the stroke length is not what is critical for lateral ink movement but the speed of the roller moving lateral is. The thick ink film just splits and moves back relative to the movement of the oscillator roller. One rotation of the oscillator roller might move laterally only a fraction of a mm. It is a very interesting thing to observe but it is important to understand.

Anyhow in the upper roller train you do not want to even out the ink distribution laterally. There the oscillation should only be for avoiding ribbing. An uneven ink film distribution is required for the ink requirements of different image coverage.

In the Anicolor type devices, the anilox roller is used because it tends to provide a surface with an even ink film which is continually in contact with the form roller and it is going at press speed. A ductor roller can not do this.

More rollers in an ink train provides more ink storage but the rate of ink transport through a high ink storage or a low ink storage ink train is the same. Ink transport depends on the ink feed rate to meet the needs of the printed image.

Higher ink storage ink trains in general are slower to respond and therefore can cause more waste as one goes through the transient from one density level to the desired level.

I hope I understood and answered some of your questions.

 

[TheProcessIStheproduct]

I was thinking of a more conventional offset press - just with full-sized forms. Wouldn't some oscillators even out the ink distribution? Why is an anilox roller used in the pan on these devices? Why not a normal ductor roller?

By adding more rollers into the train, do you introduce too much ink into the ink train - more than can be pulled out?

Anilox is used to create a even "screen" of ink, again, don't think in terms of ductors and ink-keys, because you cannot set any zones or keys, which is a blessing and a curse, the idea for pleasing color process work is no keys to set, roll up in 10-15 sheets and you are good to go, becomes more difficult if you have a press check and the person wants more warmth in the skin tone, but don't let the blue go to purple, you are having to adjust density by pressure and temp globally...

 

[djcustom1]

Wow, youguys sure get dawn and dirty her. I have allways said pressman have vary big ego's I know i have been a pressman for 31 years. I have run about every press out there and hidi's are a vary good press but there are other good ons out there today. Go on komori's web site and check out there new top and bottom sheet fed.I went to komori school on a new lithron Sp and that double sided press was amazing.Any way im now back in a small shop on a lithrone 20 inch with coater and man im in heaven now.Im just trying to make a living now.

 

[vik la luna]

Not true Erik, the Anilox roller and the inking form roller have a 100% uniform ink film thinkness on them BEFORE the hit the plate. Therefore, the mechanical ghosting theory, is not possible.

Tim

if by anilox roller you mean a roller that has been engraved by laser to various cell sizes
than,yes, by virture of design the anilox is 100 % uniform
the bridge roller or registter forme smooths out voids that develop over time due to wear and tear on components other than the anilox
I m agreeing with the Heidey Guy on this

 

[Deleted member 16349]

if by anilox roller you mean a roller that has been engraved by laser to various cell sizes
than,yes, by virture of design the anilox is 100 % uniform
the bridge roller or registter forme smooths out voids that develop over time due to wear and tear on components other than the anilox
I m agreeing with the Heidey Guy on this

If you are right, explain why the form roller MUST be the same size as the plate cylinder and run in register to it?

 

[vik la luna]

If you are right, explain why the form roller MUST be the same size as the plate cylinder and run in register to it?

because the the plate needs to recover from consumption on each revolution or impression
to keep densities consistent
anilox rollers are typically metal or ceramics so they cant go directly on to the pate cylinder
if you were running a rubber or cyrel plate than there would be no need for the form roller

 

[Deleted member 16349]

because the the plate needs to recover from consumption on each revolution or impression
to keep densities consistent
anilox rollers are typically metal or ceramics so they cant go directly on to the pate cylinder
if you were running a rubber or cyrel plate than there would be no need for the form roller

Vik la luna,

Maybe there is some confusion here with what is being argued.

One side of the argument was stating that the form roller had a uniform ink film while my view was stating that the ink film on the form roller was not uniform everywhere. It was only uniform in the image areas of the form roller.

So when you said that you agreed with the Heidie guy, I was assuming that you agree with the point of view that thinks that the ink film on the form roller is uniform. That is why I asked if you could give a reason why the form roller MUST be the same size as the plate cylinder and be in register with it. Basically geared to the plate cylinder.

If the anilox roller provided an even ink film to the form roller, then there would be no need for the extra complication of having the same diameters and being in register.

Of course you are right about anilox rollers related to flexo plates but that is a totally different situation.

Are we talking about the same think?

 

[TheProcessIStheproduct]

same size...

same size...

the form would not have to be the same size or geared, but you would want it to be so you don't have to deal with gaps, even a great anilox setup is not going to provide perfect density, especially if you have a large screen or solid and a small roller that repeats a couple times over the plate, a form the same size as plate and geared would help this problem