SM52 ink train

[RGPW17100]

We have a 2004 SM 52. Some of our jobs have a very low amount of ink to print and I find it difficult to maintain ink densities. We have multiple options

1 Short ink train
2 full ink train
3 integrated water
4 segregated water

Will using the short ink train and having the water segregated help me maintain better ink densities when running jobs with minimal ink. These jobs might included letterhead that might only have a small logo (4 color process)

I find running large solids is much easier on this press. If I want to drop or raise my density one or two points it is easy to achieve. Also with small amounts of ink if the press kicks off due to misfeed it takes almost 200 sheets to get the density back. Cyan seems to be the most problematic.

 

[M.P.Walinga]

Try to mix up your cyan with transparant white, this will increase your amount of ink on the rolers. Good luck

 

[Deleted member 16349]

Also with small amounts of ink if the press kicks off due to misfeed it takes almost 200 sheets to get the density back. Cyan seems to be the most problematic.

RGP,

Low coverage is one of the most difficult density control conditions and this is for many reasons, such as ink feed control, ink storage on rollers and lateral ink transport via the oscillators.

I would not be able to say how any of the settings you stated would affect the performance due to these many issues. Hopefully someone with direct experience with that press will be able to help.

What I would like to know is that when you state that it takes 200 sheets to get back to colour, what specifically is the problem with density. Is it too high after starting or too low or just has a lot of variation before it settles down? Is it always the same pattern to the problem or different on different jobs with low coverage?

The different results might suggest what is happening and what could help.

 

[TheProcessIStheproduct]

If you have extra room, put a couple 1/4" to 1/2" take off bars at the end of the sheet, it will really help control ink on those very light coverage jobs, even on the big presses we have this problem, because it is very rare these days that we are not painting the sheet so a LH job can be more work then a full coverage pocket folder....

 

[Ret Heidelberg Instructor]

Have you checked your night latch position on the dampening unit especially in the cyan unit? You may be need to make an adjustment. When you shut the press down and drain the air off at the feeder, check and see if you have a clearance of .004 thousands of an inch or .10 of a millimeter between the water pan roller and the chrome metering roller. If the gap is to big you will get too much water in the dampening unit when the press trips off and you to re-start into production. The setting screw is in an awkward place and you will have to use a 5mm Allen wrech with a ball end to turn the set screw. Hope this helps.

 

[RGPW17100]

Have you checked your night latch position on the dampening unit especially in the cyan unit? You may be need to make an adjustment. When you shut the press down and drain the air off at the feeder, check and see if you have a clearance of .004 thousands of an inch or .10 of a millimeter between the water pan roller and the chrome metering roller. If the gap is to big you will get too much water in the dampening unit when the press trips off and you to re-start into production. The setting screw is in an awkward place and you will have to use a 5mm Allen wrech with a ball end to turn the set screw. Hope this helps.

I will look into this. When feeder causes a restart say double sheet, late sheet what ever. Once you restart the feeding process the water goes real high. Cyan density will drop to 50 then after 200 sheets the water and ink balance out to around 125 where I normally run it. High coverage area is not a problem. Usually then I can get color back within 50 sheets. Your explanation sure makes sense. Things are slowing a bit so hopefully I can look at it tomorrow. I will bring is a set of feeler gauges and see what I see when the air is bled off.

 

[Ret Heidelberg Instructor]

If your dampening is set properly with the night latches set correctly you should be back to color in in about 15 to 20 sheets on average to full coverage. In my opinion 50 sheets is too much and this was a problem back when the SM 52 was introduced. Customers were complaining about wasting too many sheets on start up or after a press trip off. There was a services bulletin that addressed the the problem and I even saw it some older operator manuals. Also check your pre-dampening and post dampening settings. You say that you have a 2004 model, so you should be able to set the post dampening to come off right after the press trips off if you so desire. If you want to see what happens with the dampening unit when it is engaged try this. Take a trouble light and shine it into the dampening unit and observe what happens, When the unit engages you will see the pan roller overspin briefly. If the the night latch gap is too big you will see a lot of dampening solution. If they are set correctly you will see the overspin but not a lot of solution flying around. You can do this one unit at a time to see what happens. Post your feedback it might help others experiencing the problem. Good lick.

 

[Deleted member 16349]

Once you restart the feeding process the water goes real high. Cyan density will drop to 50 then after 200 sheets the water and ink balance out to around 125 where I normally run it.

RGP,

I have a suggestion for a test that might be of interest when printing the low coverage image on your cyan unit. It can be done before or after you inspect the dampening unit.

The test would be to have the ductor stopped when you restart and leave it off for about 10 to 20 sheets and see what happens to the low coverage print density.

 

[Dan Roll]

I agree with M.P.Walinga with one small difference. When running very light coverage it is always helpful to increase the vehicle content of your ink. Add regular clear gloss varnish to the ink and everything should get better. Do not be shy about it; 10 to 15% is where I would begin. I have watched people add as much as 40% and have their density go up. The concept is that the transfer will improve faster than you are diluting the color.

 

[Deleted member 16349]

I agree with M.P.Walinga with one small difference. When running very light coverage it is always helpful to increase the vehicle content of your ink. Add regular clear gloss varnish to the ink and everything should get better. Do not be shy about it; 10 to 15% is where I would begin. I have watched people add as much as 40% and have their density go up. The concept is that the transfer will improve faster than you are diluting the color.

Dan,

Would this suggestion be a problem with printing an image that has mixed coverages a bit isolated from each other. Where there is very low coverage on one side of sheet and high coverage on the other side (gear side vs operator side)?

 

[Dan Roll]

Dan,

Would this suggestion be a problem with printing an image that has mixed coverages a bit isolated from each other. Where there is very low coverage on one side of sheet and high coverage on the other side (gear side vs operator side)?

If the ink water balance is narrow, if the density is unstable, if the density is lower than desired, or if the ink is emulsifying in the roller train, adding varnish should help, if not solve, the problem. The primary shortcoming of lithography is light coverage, that is why some specialty presses include a unit or two that prints intaglio or some other process where light coverage is routine. The presses the US prints postage stamps are an example, although they no longer print the price on the stamps which led to this requirement.

 

[meddington]

Low coverage is one of the most difficult density control conditions and this is for many reasons, such as ink feed control, ink storage on rollers and lateral ink transport via the oscillators.

This also leads to an issue with regard to aiming at process control targets with heavily GCR'd imagery. Often with heavy GCR the cyan separation is very skeletal (depending on the subject matter), and due to light coverage, the SIDs tend to fluctuate more. This makes it more difficult to hit target SID for cyan, but often doesn't have a profound visual effect on the imagery (as the channel is skeletal). Makes it more difficult for pass/fail based on measurements (somewhat popular with software vendors now days), but easier for visual pass/fail. Traditional separations (fully coverage) are a bit more stable in terms of density adjustments, but the separations are therefore more susceptible to variation. Sorry...a bit off topic.

 

[Deleted member 16349]

This also leads to an issue with regard to aiming at process control targets with heavily GCR'd imagery. Often with heavy GCR the cyan separation is very skeletal (depending on the subject matter), and due to light coverage, the SIDs tend to fluctuate more. This makes it more difficult to hit target SID for cyan, but often doesn't have a profound visual effect on the imagery (as the channel is skeletal). Makes it more difficult for pass/fail based on measurements (somewhat popular with software vendors now days), but easier for visual pass/fail. Traditional separations (fully coverage) are a bit more stable in terms of density adjustments, but the separations are therefore more susceptible to variation. Sorry...a bit off topic.

This is of interest to hear how prepress methods affect the requirements of capability at the press. Thanks.

I pretty well understand the problem from the press side and know what needs to be done to tightly control density for low coverage. Part of this problem was discussed in my 1997 TAGA paper.

 

[3rd shift Bill]

If you are seeing a 75 point drop in color on your cyan on restarts after the feeder trips off you are getting to much water on the plates and you can go to your console and change the predampener settings to reduce the number of revoltions the dampner runs before the unit engages and goes on impression.

 

[neleson]

Hi All,


Nice discussion guys.. but i am totally agree with Heidelberg.


_________________________________
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[Ret Heidelberg Instructor]

Ret Heidelberg Instructor

Ret Heidelberg Instructor

Just curious. To the original poster RGPW1700. How did you make out with the problem?

 

[turbotom1052]

if you have room on the sheet i would suggest as much take off bar as you can fit in order to get a decent flow of ink in and out of your inker. Ive found that light coverage jobs tend to cause the ink to sorta stagnate in the rollers. A good flow in and out of your inker will assure fresh ink with a much more stable emulsion. The suggestion to shorten ink train and run water system segregated will help too.
another suggestion would be to have the vibrator rollers stop their side to side motion when the unit kicks off impression. I dont know if this is an option on a speedmaster 52 but on the larger speedmasters you can set it up in cpc 2000 to do that

 

[mrrapid]

Charge Bars

Charge Bars

We have the same problem. I think everybody does. However what we do is put a charge bar down to help with the light ink coverage. It's kind of like a color bar but it''s just a long far bar that goes across the width of the sheet by the color bar to give the sheet some ink instead of having almost nothing on it to print. It really helps make our lives easier. If you have room on the paper which you should with a 12.5x19 sheet or bigger, you should try it. It will help you! Good Luck.

 

[RGPW17100]

Really have not been able to look into it. Our press operator was gone for 2 weeks and I was covering for him. I spoke to him about it and he feels just like everyone here is saying that it is a pain but he does drop his water a lot when the press kicks off then slowly brings it back up. We compared the night positions of the the meter to pan rollers and found them all to be less then 4 mils. In a way I am glad he is back but it sure a lot nicer machine then the GTO and quick master.