mechanical ghosting

[rich apollo]

A question regarding mechanical ghosting. If your ink form were the same diameter as your plate cylinder, wouldn't mechanical ghosting be eliminated?

If this is correct, why have offset presses evolved the way they have, with multiple small form rollers?

 

[jdaghir]

Yes, that is correct. See the KBA Genius 52 for an example of this. Why do most presses have multiple small form rollers? That I can't answer.

 

[Cornishpastythighs]

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?

 

[Deleted member 16349]

A question regarding mechanical ghosting. If your ink form were the same diameter as your plate cylinder, wouldn't mechanical ghosting be eliminated?

If this is correct, why have offset presses evolved the way they have, with multiple small form rollers?

A single in register form roller on its own is not sufficient to prevent mechanical ghosting. For the single form roller concept that is used in Anicolor, Karat, etc. the ink film on the form roller is not uniform everywhere. The non coverage areas on the form roller has a thicker ink film than the image areas. With this concept, the roller that supplies ink to the form roller MUST have a uniform ink film everywhere. That is why an anilox roller is used. The intention is to uniformly ink the image areas of the single form roller.

If you supplied an in register single form roller with a conventional roller train set up, it would not be very difficult to uniformly ink the image area. Also mechanical ghosting patterns could come back onto the single form roller, in image areas, from the supply roller.

There are other ways to use a single form roller concept but it would not have to be an in register concept. With a not in register concept, the ink film on the single form roller MUST be uniform. This would result in no mechanical ghosting. This can be approached in different ways.

The multi form roller design is probably a result of tradition and rule of thumb design as anything. It worked well enough and as long as printer bought it, why should the press manufacturers change. Customer demands in performance will have an affect on technology development. If you don't complain there will be no change.

The devil is in the details of any approach taken. One can not just change one thing and expect a positive change. With roller trains, everything affects ever other thing.

 

[Al Ferrari]

See the KBA Karat and the 74G as in addition to the Genus 52. Note that Heidlberg has discovered this also for their Anicolor presses.

KBA Karat - Google Search

KBA 74G - Google Search

Anicolor - Google Search

Al Ferrari

 

[The Heidelberg Guy]

A single in register form roller on its own is not sufficient to prevent mechanical ghosting. For the single form roller concept that is used in Anicolor, Karat, etc. the ink film on the form roller is not uniform everywhere. The non coverage areas on the form roller has a thicker ink film than the image areas. With this concept, the roller that supplies ink to the form roller MUST have a uniform ink film everywhere. That is why an anilox roller is used. The intention is to uniformly ink the image areas of the single form roller.

If you supplied an in register single form roller with a conventional roller train set up, it would not be very difficult to uniformly ink the image area. Also mechanical ghosting patterns could come back onto the single form roller, in image areas, from the supply roller.

There are other ways to use a single form roller concept but it would not have to be an in register concept. With a not in register concept, the ink film on the single form roller MUST be uniform. This would result in no mechanical ghosting. This can be approached in different ways.

The multi form roller design is probably a result of tradition and rule of thumb design as anything. It worked well enough and as long as printer bought it, why should the press manufacturers change. Customer demands in performance will have an affect on technology development. If you don't complain there will be no change.

The devil is in the details of any approach taken. One can not just change one thing and expect a positive change. With roller trains, everything affects ever other thing.

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

 

[Deleted member 16349]

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

Sorry you are wrong. If what you say is true, there would be no need for an in register form roller.

 

[The Heidelberg Guy]

Sorry you are wrong. If what you say is true, there would be no need for an in register form roller.

Being that I was involed with testing and was one of the few Instructors on the Anicolor, I guess we are all wrong. Incredible...........

 

[Deleted member 16349]

Being that I was involed with testing and was one of the few Instructors on the Anicolor, I guess we are all wrong. Incredible...........

Go talk with the Heidelberg engineers. Maybe they don't really know either. Yes you are wrong.

As I said, a non in register single form roller would ghost when supplied by a anilox roller. That would confirm that they ink film is not uniform everywhere. It must be in register to avoid the ghosting due to the non uniform inking of the form roller.

 

[The Heidelberg Guy]

Go talk with the Heidelberg engineers. Yes you are wrong.

Have you ever even ran a printing press? How many years?

If engineers were so accurate, they wouldnt need testing now would they?

 

[Deleted member 16349]

Have you ever even ran a printing press? How many years?

If engineers were so accurate, they wouldnt need testing now would they?

I might have to agree with you on this. Heidelberg engineers are not so good as to produce predictable performance.

 

[The Heidelberg Guy]

I might have to agree with you on this. Heidelberg engineers are not so good as to produce predictable performance.

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

 

[Deleted member 16349]

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

I am an engineer. I know how to calculate ink film thicknesses on roller trains.

What is your evidence that there is a uniform ink film on the form roller? The non image area of the in register form roller is never seen on the printed sheet. So how do you know that the ink film is uniform?

Some people have all experience and no theory. Just opinions without evidence.

 

[J]

The Wright Brothers had never been airplane pilots but that didn't stop them from designing the first airplane.
I doubt that any of the engineers designing equipment for the graphic arts industry has ever worked with that equipment in a production environment. To have done so would probably be more of a hindrance than a benefit.

J

 

[Deleted member 16349]

The Wright Brothers had never been airplane pilots but that didn't stop them from designing the first airplane.
I doubt that any of the engineers designing equipment for the graphic arts industry has ever worked with that equipment in a production environment. To have done so would probably be more of a hindrance than a benefit.

J

J,

Actually I was involved with print production, not as an operator but as a production supervisor/process engineer. I did a lot of testing, observing and thinking about this process. It is very important to be close to the actual process and it was also very important for me to develop theoretical reasons for how the process works.

Yes the Wright Brothers got things going based on some theory but also some testing of kites and testing concepts in a wind tunnel. They did pilot gliders first. They also used their experience to continually improve the knowledge.

Questionable theory without experience is not good and experience without valid theory is not good for improving the process. The goal is to develop valid theory that predicts performance. Experience supplies the problems to work on and it also is used to validate or invalidate theory. Experience on its own is useless for innovation.

 

[Al Ferrari]

"Some people have all experience and no theory. Just opinions without evidence."

Let's slow down a bit. That last statement seems to say that the theory is the evidence and that the opinions are the experience. Probably not what was intended.

Al

 

[Alois Senefelder]

Ghosting

Ghosting

Hello fellow Lithographers and Mr. Erik Nikkanen,


A PDF - Ghosting - Mr E. Nikkanen what do you mean by "in register forme roller" ???



Regards, Alois

" I am not ashamed to confess that I am ignorant of what I do not know" ---

Marcus Tullius Cicero

 

[Al Ferrari]

The plate and blanket are in register because they are the same size and thus any spot on the plate will always come back around and be on the same location on the blanket. Likewise, on presses having a single ink form of the same diameter as the plate cylinder, a spot on the form roller will always be on the same location on the plate.

One place to read up about this, would be the KBA site, but there are probably others.

Al Ferrari

Edit: Here is an interesting, and apparently independent review of the 74 Karat:

KBA 74 Karat Advice - Color Printing Forum

 

[Deleted member 16349]

"Some people have all experience and no theory. Just opinions without evidence."

Let's slow down a bit. That last statement seems to say that the theory is the evidence and that the opinions are the experience. Probably not what was intended.

Al

Yes Al. You are right. It is not a correct comment.

If one wants to prove a theory, one needs some kind of evidence and ways to test the theory. Opinions without evidence is not good nor is theory without a proof. Poor assumptions are usually at the heart of poor opinions.

Al, would this be acceptable?

 

[Deleted member 16349]

Likewise, on presses having a single ink form of the same diameter as the plate cylinder, a spot on the form roller will always be on the same location on the plate.

KBA 74 Karat Advice - Color Printing Forum[/url]

Al, I would add that the single form roller of the same diameter probably must be geared to the plate cylinder for accurate register. The diameter being the same is no enough. I am assuming you knew this but I just wanted to clarify.

Great reference on the Karat press review. It is not often that one can get such a list of observations that one would normally never hear about. Thanks.