Ink key presetting

[Deleted member 16349]

A bit of a trivia question to get the thinking process going.

The ink key meters ink onto the ink fountain roller as the ink feeds in the gap between the ink key tip and the moving fountain roller surface.

What percentage of that metered ink actually goes into the press roller train?

 

[Alois Senefelder]

Ink Splitting

Ink Splitting

Erik,


And the answer is !!!!!! a PDF




Regards, Alois

 

[Deleted member 16349]

Erik,


And the answer is !!!!!! a PDF




Regards, Alois

No, I don't think so. You were saying a 50-50% split but that did not really answer the question. Also the diagram is not clear.

Any other guesses from others? There is no exact percentage value. I am trying to see if people have an idea of the approximate range.

 

[Alois Senefelder]

Again !

Again !

Erik,

Again I will tell you - that what ever the volume of Ink on the Duct Face, 50% will be

transfered into the press roller train.

The schematic of the Ink Profile, is from Heidelberger Druckmaschien AG



Regards, Alois

 

[Deleted member 16349]

Erik,

Again I will tell you - that what ever the volume of Ink on the Duct Face, 50% will be

transfered into the press roller train.

The schematic of the Ink Profile, is from Heidelberger Druckmaschien AG



Regards, Alois

OK let's look at what happens on press.

The ductor roller moves back and forth between the roller train and the ink fountain roller. Let's say that the ductor is in contact with the roller train 50% of the time and is in contact with the ink fountain roller 50% of the time.

So this means that at least 50% of the ink on the ink fountain roller does not even get touched by the ductor as the ink fountain turns.

When the ductor is in contact with the ink fountain roller one could say that there is a 50% split. That does not mean that 50% of the ink on the ink fountain roller gets transferred since there is also an ink film on the ductor. Therefore less than 50% of the ink film would get picked up by the ductor.

This brings us down to less than 25% of the ink metered by the ink key onto the ink fountain is actually transferred to the roller train. This is if all goes according to some simple model of how things work.

But things are not so simple in real life. Ink transfer via the ductor is not only in one direction. When the ductor contacts the ink fountain roller the fresh ink metered by the ink key mixes in the nip with the water logged ink from the roller train. The ink flow is in two directions. This can be easily seen when contaminated ink from other units, gets into the roller train. It will quickly end up in the ink fountain.

When the ductor, which is rotating quickly, it must come down to the surface speed of the ink fountain roller at contact, ink can be momentarily scrapped from the surface of the ductor roller and form a slight bead of ink. This can affect the percent of ink transfer.

Also it is common knowledge that temperature variations will affect the net transfer of ink into the roller train. With waterless presses this is commonly understood but seems to be forgotten with lithographic offset.

The point I was trying to make is that that actual amount of ink transferred into the roller train is relatively small (<25% range) compared to the total amount of ink metered by the ink key. It is also variable due to many factors.

Consistency of ink transfer is just one area that makes presetting difficult with the existing conditions on press.

 

[Al Ferrari]

Alois,

You have been around these forums long enough by now to know that Erik has thought a very great deal about this topic of ink transfer from the fountain roller to the ink roller train. You are in beyond your safe depth taking on Erik on this topic. Instead, you should look up all his posts on the subject, both here and elsewhere. I think you would find it well worth your time.

Al

 

[Al Ferrari]

Everyone please note that Erik is not talking about ink transfer in general in the ink roller train where that 50/50 thinking might be applicable, but between the ink fountain roller and the ductor roller. The key to the argument is in realizing that the ductor roller's relations to the fountain roller, and to the rest of the ink roller train is totally different than the relation between any other roller pair in the ink train.

Al

 

[Cornishpastythighs]

Ink key presetting to me is about what your expectations are of a flawed system. I don't expect to be at 90% colour on my first pull like they show you at the printing shows. We spend a lot of time and effort making sure our ink keys are operating properly and zero set to manufacturers specs. We also spend a lot of money making sure our inking rollers are in good condition and set correctly and our dampening system is working correctly. Even with all this effort our CIP3 presets only give us fairly even settings and somewhat acceptable colour.
It is however far better than having nothing and our press guys would be screaming if they had to manually set the ink keys for every plate so they must be getting some benefit out of presetting.

 

[rich apollo]

Worked with a press the other day that had no ink fountains, fountain rollers, or ductors. Instead the ink was pumped directly onto the metering roller. Probably old hat to many of you, but it was new to me.

 

[Deleted member 16349]

Yes, a 50-50% split is commonly used in analyzing roller trains. It is a convenient ratio even though it most probably is not actually true. The actual split can be affected by many factors.

If there is a difference in temperature between rollers in the roller train, such as between the smooth hard rollers that have cooling and the soft rubber rollers, there will probably be a difference in the split ratio.

There is probably a difference in split ratio between a hard roller and the soft roller contact.

There is probably a difference in split ratio due to differences in the amount of water content in the ink film on the rollers. Water comes up from the plate in the ink films, while fresh ink comes down. It is reasonable to think that it will be easier to split more in the water logged ink film than in a less waterlogged ink film.

But 50-50% split ratio is used because it is easier to calculate and gives a general idea of how the ink is distributed on the roller train. In calculating the ink distribution, each nip is given an equation. The two ink films coming into the nip are added and then divided by 2 (50-50% split) to determine the exiting ink films on the two rollers.

Why would one use this equation? Well it is due to the conservation of mass. The ink entering the nip must equal the ink exiting the nip. For some reason, the press engineers can understand this concept for a nip but don't understand it for the whole press.

Ink Transfer

Even if we assume a 50-50% split ratio, the split ratio has NO direct relationship to the amount of ink transferred. A large amount of ink can be transferred, a small amount or no ink can be transferred or even a negative amount of ink can be transferred, all with the same 50-50% split ratio.

And this gets back to the heart of the presetting problem on offset presses. Trying to account for all the issues that prevent predictability on existing presses will not fully solve the problem. The press must be modified in a way so that it is feeding ink consistently and predictably and is independent of those factors mentioned earlier. When that is done one can apply the proper algorithms to set the key values etc.

The problem is complicated but not actually difficult to solve.

 

[Green Printer]

Interesting concept. Variable cuim no ink sliders or keys required.

Printing Automation Systems-I.Mer Co., Ltd

 

[Deleted member 16349]

Worked with a press the other day that had no ink fountains, fountain rollers, or ductors. Instead the ink was pumped directly onto the metering roller. Probably old hat to many of you, but it was new to me.

Pumped zoned ink feeds have been around for probably more than thirty years and have been used mostly for offset newspaper presses. There have been several different configurations, most all having some issues. The details of how they were designed can make a difference in their performance.

Can you give any details the system you were looking at?

Thanks

 

[Green Printer]

Various presses using the undulating ductor


http://m.youtube.com/watch?v=xqFq0gxfdjE&desktop_uri=/watch?v=xqFq0gxfdjE

 

[Al Ferrari]

Colorful images and obnoxious muzak, but no explanations.

Al

 

[Deleted member 16349]

Various presses using the undulating ductor


http://m.youtube.com/watch?v=xqFq0gxfdjE&desktop_uri=/watch?v=xqFq0gxfdjE

Thanks for posting this concept. I think I have seen this in the past but I took a closer look at it now and I have to say there are some interesting features with this concept.

I really like the idea that with this concept, a zero set is really a zero set. This is a big deal in my mind.

I think it will also tend to have less contaminated ink and water going to the ink fountain due to the reduced contact time with these ductor on lower coverage. That is also positive in my mind. Not sure how it performs in practice though.

Since the ductor segments acts as ink keys or zones, one issue might be that they are wide.

I would worry about how the segments clean up. Would residual ink get caught in the gaps and contaminate runs after colour changes?

The operation of a timed binary (on off) ductor segment would be cheaper to manufacture than the existing proportional control of ink keys that now are used. Manroland had a patent with binary ink key, which I liked in principle. Driving the ink feed with a timed binary method would also be more accurate in my opinion than proportional control.

This concept would not address the ink water balance issue since it is no a positive ink feed system. It is a very interesting concept but one that falls short of what I think is the full potential.

Glad you posted it. I do agree with Al, the music is hard to take.

 

[Cornishpastythighs]

Bit of history on the Baker Perkins Undulating inking mechanism
This has been around for a good many years now.

C.U.I.M. - the Continuous Undulating Inking Mechanism - a Patented Aller design to overcome the mechanical shortcomings of the traditional transfer roller oscillating between the slow-speed duct roller and the first drum of the inking system. It comprised a series of free-running rubberised discs eccentrically-mounted on a common drive shaft, with the eccentric centres equi-phased to each other. The effect was to progressively transfer ‘strips’ of ink (the width of each disc) to the first drum, by rotation only. The arrangement was so successful, that it was subsequently used on the full PMD product range (except the Jupiter double-width Newspaper units), although limitations became apparent with the high speeds achieved during the 1980’s and later. It was finally overtaken by Continuous Inking - a fixed transfer roller, set to very fine clearances (c.0.075mm) with duct roller and first drum - with the advent of the Rockwell G25.

 

[Prepper]

Ok, so if using a manual system, where the press is supplied with a printout of what to set the keys to, wouldn't that mean that they would also have to set the press to the same sweeps at startup every time and the key openings control the amount of ink going in? Or in other words, with this type of manual system, it would never work if the pressman changes the sweeps up and down according to how he sees the coverage and applies the key presets and starts up?

 

[Alois Senefelder]

C U I M inking

C U I M inking

Gentlemen,


re CUIM inking system, it does require a Ink Duct Pre- setting system via Slides or Keys


3 PDFs should you still be interested !



Regards, Alois

 

[Deleted member 16349]

Bit of history on the Baker Perkins Undulating inking mechanism
This has been around for a good many years now.

C.U.I.M. - the Continuous Undulating Inking Mechanism - G25.

I hope people understand that the system Green Printer referred to (PAI-I.Mer Co) is quite different from the Baker Perkins C.U.I.M mechanism.

 

[Green Printer]

The segments on this ink ductor work independently of each other. The ink film on the ball is a constant. All you do is change the contact timing. Again each ductor segment is independent. The CUIM invented by Mr. Aller was a breakthrough it operated as a singular unit. This unit is the next breakthrough in ink control.