CP2000 characteristic curves for ink presetting

anyone know how to set the preinking curves in cp2000 for

 

It is my feeling that pre inking should be done with an even film of ink across the entire roller train, on all units. The type of coverage on a form, and the location of images across each unit, should not even be a consideration when doing the original ink up of the press. Characteristic curves and zonal differences in ink flow ONLY come into play once sheets start printing. And inker should always deliver zonally, just what's needed to replenish what's used after impression. If you can wrap your mind around this thinking, you will find a greater understanding of the entire process. Lets assume for a minute that pre press has done its job correctly, and delivered to you plates that are imaged with the right dot structures on ALL colors. These "correct" plates should in theory, AND in practice, allow you to run an even and repeatable ink film thickness across the entire width of the press, and consistency from unit to unit. This consistency should also be from one form or job to the next. Quality and consistent printing counts on this. On any given job you should be able to either measure, or visually see an even ink film across the length of the rollers. Every pressman should strive for this even inking across the entire width of the press, and from unit to unit. If you are having to run visible areas of thicker ink in some zones than in others, then you have a problem with pre press. This even inking is what makes it possible to deliver color consistency and has an influence on most every aspect of the printed job. Uneven ink films across a presses roller train is the main culprit for problems such as dry ups, washouts, setoff, hickeys, poor drying, the list goes on. The press operator who is incapable of grasping what I'm saying here will NEVER amount to anything more than a button pusher. The ones that know what im talking about here will becomes the leaders in their field.

 

I dont totally agree with you tom.

Job to job area coverage can vary a LOT. Prepress cant do the slightest thing about it.
If lets say zone 1-3 have a 50% tint and at 4-10 a full solid -all units or not- you MUST push those zones higher to get the proper density right? Also when this job reaches its total production, if it should happen your next job is just letters or your TAC is less than 50% you will have zones 1-3 a fair amount of ink -if not a bit too much- but at 4-10 you have an overexcess of ink that can almost never get down to proper density, unless pressman prints sheets with previous plates and no ink feed for n sheets until he clears the excess ink.

 

This is exactly what im talking about. Ill quote you when you say this..."You MUST push those zones higher to get the proper density right?" If your referring to "pushing" the ink feed into the inker then Id say yes. Its a no brainer that you would have to feed more ink into the inker in line with a big solid. The point that im making is this....This "pushing" of ink from the fountain in certain zones, although absolutely required to print a big solid on half of the sheet, should have ZERO effect on the ink film thickness present on the rollers when starting and during a production run. The pushing of ink in high coverage zones only serves as a means of replenishment of the ink required for the form. Lets say that your running a form with a big gripper to tail 4color image on the near side of the press. Your fountain keys in line with that image are all opened to say 12 diodes. The other side of the sheet has a small 1"x1" square of 4color process requiring a fountain setting of just a single diode. If you were to stop a job that's under production conditions with perfect ink water balance, with a dead stop, and then go up to the printing units you would find that (as long as your pre press dept has the plates dialed in correctly) that the visible ink film as seen on the number 4 form roller will be the very same ink film on the full coverage side of the press as the ink film thickness of the light coverage side of the sheet. There should be no difference in what you see on the form rollers. The color bar SHOULD read the same in line with the big solid as it does with the small little image. The very fact that the color bar reads the same is an indication that the ink film thickness is the very same. Therefore... when first inking up a press in the morning you should be inking it up evenly across the entire width of the press. If your pre press CIP data is accurate then you will require minimum adjustment but at the end of the MR you should have even ink film thickness across all units. Your ink fountain opening may vary greatly but under running conditions up to color your ink film thickness on the form rollers should be the same. When it comes time to begin MR on the next form the very same ink film thickness that is on the inker from the first job should be the proper ink film thickness for the next job regardless of the coverages. You will of course have to load the new CIP date into the press so that the fountain reflects the new form requirements but technically if your new forms fountain settings are dead on accurate you should be able to maintain the same ink film thickness on all units. We all know this rarely happens but in theory it could.

 

I had this very discussion with a co worker many years ago where in order to prove my point about ink film thickness I did this experiment right in front of him. I took used plates of a 4color job id printed, were I knew that the press in the past printed the job with good color, with the same even ink film thickness, as visualized on the rollers. This was over 30 years ago when the press I was running did not even have a console. It was manually adjusted ink keys right at the fountain. Initial settings were made by looking at the mounted plates and adjusting ink keys to come close to what I thought was close ink settings as viewed from the fountain openings. An even film of ink was tapped on to all four units and the press was allowed to idle for awhile to distribute the evenly tapped on ink to all four inkers. After fitting all four units of the job I proceeded to run a lift of about 100 sheets of waste. At this point without ever even looking at a sheet, I would go up to each of the four printing units and make fountain key adjustments based only on a visual inspection of the ink film on the number 4 form roller. Of course it required a bunch of books of waste but I was able to get a very close color match to the original printing without ever looking at a single sheet. This is not being mentioned to show how great I am but as a way to prove my point about the importance of fully understanding the concept of consistent and repeatable ink film thickness.

 

Dear Ashok
All what other gentlemen were mentioned about is right.
But if you mean the numbers of how much pre inking number for each unit you need confirm me please.

 

I never liked very much Heidelberg's pre inking protocol. As I remember they were set up to start out with an even duct up profile and then resorted to a few zonally adjusted ducts taken from the CIP data. I always made it a point to create my own ink up profiles that were as mentioned EVEN. The only alteration I made in my ink up procedure was to allow a couple more ink ducts if I were printing on an uncoated sheet.

 

Everyone knows that ink doesn’t move instantly from the ink well to the plate - it must first travel through the roller train. So in order to print both heavy and light coverage areas, you’re going to need to carry more ink on the rollers in some areas, and less ink on the rollers in others. If everything else in the printing process is correct, the ink film at the form rollers will simply be whatever is needed to print what’s imaged on the plate.

 

Which file is better to use to adjust curves? Covering shapes, what should be the plot drawing??? For printing plate

 

Hi printers o/ i am a print finisher looking for a diagram that will explain the the gripper transfer between sides of print. Please excuse me. I am a dumb guillo operator that is interested in the affect sheet size variation plays in perfecting. Thank you for any response.

 

And in general I also agree with Turbotom in regards to any machine. You can never trust the make ready sheets. Machines... especially Heidelberg behave differently on the run.

 

The issue with a gripper to tail sheet size variation when perfecting is that when the perfector unit flips the sheet, its being grabbed, or perhaps even NOT grabbed, in the same spot. This variation in sheet length can cause either dropped sheets or nicked sheets. Registration should remain accurate front to back as long as the sheet position is being held with the perfector suckers on storage drum. If size deviation is too much it will result in either dropped sheets or nicked sheets. As a cutter operator you need to understand that variation of as little as 1.5mm can cause problems. The pull of the knife when cutting a full clamp of paper, is enough to cause that much variation.

 

Dear Tom.
The concept of the Preinking curve is that you can can be very close to the desired ink density faster.
Let's say that you begin with 30 ink duct, you want these 30 ink duct to result (almost) of what you have in your ink profile, now print 200-300 sheets (depends on the image area you are printing) then stop the machine and compare the density of sheet no.50 with the density of sheet no.200-300.
If the density is increasing then your 30 ink duct was low and you have to increase it, and vice versa.
Regards

 

Hi Tom thanks for the response. Now I am going to sound stupid when I ask definitions of the terms of "dropped sheets" and "nicked sheets". Recently was asked to cut stock on a blunt blade. But I was also under the impression perfectors could tolerate up to 3mm in sheet variation. However I was interested in the transfer of the sheets is there a moment in which they are not mechanically held and where they are actually released and pneumatically held ? I am interested to know if a sheet varies up to 3 mm on a heavy stock why is it a problem, sorry I know its a problem but can't it be compensated for? in general perfectors have a 15-20 mm grip edge so in grip transfer logically should that not allow for a huge amount of variation in the sheets ?
Generally speaking stock can range up to 2.5 mm variation depending on the weather... this is why I asked for a diagram explaining the sheet travel. I am also unfamiliar with printing machines "storage drum" is this the point which the sheet changes grips ? Please excuse my dumbness. And HAGO o/

 

Also I am a very careful cutter and do not put full clamps of paper in. IMO that is crazy. i see how much the knife is dragged out. People who do that trying to save time only waste time. I am only asking because my boss said i should have pulled the job and done a knife change. My problem was and still is I'm fresh back to work after 4 years away and was not keen to do a knife change and am and probably still will be a casual operator.
But strictly speaking 1.5 mm is maximum tolerance on sheet size perfecting on 10 colour press ?
Sorry for blabbing. 1.5 mm and I should pull the job full stop ?

 

@Krispy
If you really need to know the exact number, you could always check the operator book to verify the recommended amount. I think that maybe the most important thing is just trying to maintain as little to no cutter draw as possible.

From feeder to delivery, I don’t think there’s a time when the press grippers ever let go of the sheet entirely, and that includes at the perfecting unit. The vacuum on the cylinders there is mainly to keep the tail of the sheet down and against the storage drum, so that it transfers correctly when it’s being reversed...