Color Variation on Same Sheet

Discussion in 'Heidelberg Printing Presses' started by Fawzi_Albasha1, Dec 28, 2021.

  1. Fawzi_Albasha1

    Fawzi_Albasha1 Member

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    Hello,

    I currently have an issue on 1 Printing Unit of the 4-Color SpeedMaster.
    When printing all over the sheet, no matter the size, there is always a color difference in the first 10 cm of the sheet (starting from the gripper).

    I have attached an examples image for reference.

    When placing the printing plate on another unit, the issue is gone.

    First I thought it should be one of the plate inking rollers, I started by disconnecting one roller at a time, but the same issue keeps on appearing.

    Then, I replaced the plate dampening roller, but no luck.

    Then I checked and re-adjusted the rollers once more but did not succeed.

    Any suggestions one what could be the issue?

    Thank you.
     

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  2. jwe

    jwe Member

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    maybe packing under blanket.
     
  3. mantman

    mantman Senior Member

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    1. You could change the oscillation of form rollers -release the 1st and 3rd- or stop them from moving side to side.
    2. Try printing a full solid with no water to see if it still persists and exclude water issues
    3. Change the timing of oscillation from D.S. -the white and red numbers-
     
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  4. Fawzi_Albasha1

    Fawzi_Albasha1 Member

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    Changing the packing under blanket did not solve the issue.
     
  5. Fawzi_Albasha1

    Fawzi_Albasha1 Member

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    What do you mean by No.3: Change the timing of Oscillation?
     
  6. mantman

    mantman Senior Member

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    If you open cover at drive side you will see gears and some disc with some numbers on it -1-5 white and red-.
    Those numbers change the timing of rollers. Your form rollers will hit closer to the middle or tail edge of sheet.
    I think red numbers change the oscillation from eg DS to OS to opposite.
    Also there are another set of numbers with circles 0-25mm which mean the motion range of oscillation. Usually max is the best -25-.
    You could check the others PU`s and do the same for PU 1 or experiment till you get a satisfactory result.
     
  7. Fawzi_Albasha1

    Fawzi_Albasha1 Member

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    I have followed your step No.2 by printing full solid with no water, the issue was gone. So I went back to the dampening rollers and started by removing the Intermediate Roller (#15) until I saw a slight difference in the position of the color variation boundary when adjusting the Dampening Distributor (E).

    I placed all the rollers back in position and started increasing the pressure between the Dampening Distributor Roller (E) and Dampening form roller (#15) until the color variation could not be detectable any more.

    The contact area line between the two rollers required to fix the issue is 5.5 mm (even though the line was at 4 mm before).

    thank you all for your help in this matter.
     

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  8. asem alsafady

    asem alsafady Senior Member

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    Please Mr. Fawzi, I just want to ask if you have vario system at your machine?
     
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  9. Tsvetan Tsaryanski

    Tsvetan Tsaryanski Member

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    I have never worked in Heidelberg. I had this problem on another machine. the cause was a broken pressure mechanism.
     
  10. Fawzi_Albasha1

    Fawzi_Albasha1 Member

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    Yes, I have Vario system on my machine, but I am well aware that the vario operation is performed to reduce the hickeys on the printing plate, not fixing the issue of having different color densities on the same print.
     
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  11. Fawzi_Albasha1

    Fawzi_Albasha1 Member

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    Which machine?
     
  12. Adil

    Adil Senior Member

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    Have you had this problem for a long time or is it a recent problem?
    From what I see it is a problem with the streaks of the cylinder
     
  13. asem alsafady

    asem alsafady Senior Member

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    Yes Mr.Fawzi, but when you have vario system it's recommend to increase the contact between the Dampening Form Roller and the Dampening distributor roller.
    And switch off the vario button at your screen when adjusting the rollers.
    So, you did the best job.
     
  14. Adil

    Adil Senior Member

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    You have to know what kind of ridges you have, there are roller ridges, channel ridges, sprocket ridges, dynamic ridges and transfer ridges.
     

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  15. Tsvetan Tsaryanski

    Tsvetan Tsaryanski Member

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    What does it matter in this case?
     

  16. Gregory Ross

    Gregory Ross Member

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    You will get a larger ink charge when the oscillation reaches the end of it's stroke. If this event occurs at the back or front of the gap, it could cause the problem. The adjustment is on the gear side, you disconnect the oscillation arm from the plate cylinder. This is a simple adjustment, some Heidelberg's are as simple as one nut but don't know your model, check manual. Move press to end of stroke, look where last over form roller is, that is where charge will start. With out moving press, loosen oscillation arm then move press and put last over form where ever you need charge to be. retighten arm. You may have to adjust again base on graphics and what you see on the sheet. have fun!
     
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