XL75 Sheet rips off and gets stuck to blanket

Discussion in 'Heidelberg Printing Presses' started by Andrei, Dec 3, 2019.

  1. Andrei

    Andrei Member

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    So were printing on 8 colour press, mostly 350gsm silk and whenever theres a solid colour sheets gets ripped off and gets stuck to a blanket which damages the blanket. Always seems to happen on black colour.
     
  2. turbotom1052

    turbotom1052 Senior Member

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    Does this always happen, or only after the press has been sitting for a bit, and you try to start up without cleaning blankets? This is not so unusual when you run job lot paper. Have you noticed this happening when you run a high quality sheet of paper? You could try giving the blankets on the solid unit, and the units that follow a light spray of anti skin spray. Only problem with that is you will be throwing away more sheets on startup and perhaps making plates a bit sensitive. Ive also had some success with starting the press up with more speed that the presses normal idle speed. If you hold down the fast button as the first sheet is heading down the feed table, you will be able to get the press to start up and a higher speed, which results in the sheet getting through the problem units quicker without sticking to the blankets. Id be careful to not start up too fast. I would think around 5000 sph would be about right.
     
  3. Andrei

    Andrei Member

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    Thia happens not only when press has been stood. Tbh press is running constantly job after job.
    Ive changed paper brand as well but still happens.
    Also have tried different speeds
     
  4. NotAGooner

    NotAGooner Senior Member

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    Have you tried a different brand of blanket maybe a quick release blanket or non-compressible blanket?
     
  5. junker1984

    junker1984 Senior Member

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    Might be a cam follower is beginning to fail.
     
  6. alibryan

    alibryan Senior Member

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    It most likely has something to do with the grippers. Especially the ones around the black colour(s).

    (Komori)
     
    Last edited: Dec 3, 2019
  7. narayan

    narayan Member

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    Does the paper always rip at same place? Check the Impression and transfer gripper tip at that place. May be needed to adjust or replace the gripper tip.
     
  8. Andrei

    Andrei Member

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    Never at the same place.
    Happens on 2 units, both black. Back side of sheet and front
     
  9. asem alsafady

    asem alsafady Member

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    I agreed with all what others said.
    But strongly agreed with Junker, check your impression cylinders cam followers, or change your ink brand to another brand with lower viscosity, especially when the weather is cold.
    Good luck.
     
    Last edited: Dec 5, 2019
  10. turbotom1052

    turbotom1052 Senior Member

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    Agree that perhaps too much tack to the black ink. Does this happen even when the black coverage is light?
     
  11. Andrei

    Andrei Member

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    Sometimes, depends on speed.
    Cant run it at full speed, de-laminates sheet
     
  12. turbotom1052

    turbotom1052 Senior Member

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    Based on some of the info you've given I would guess that your running bottom of the barrel paper. I asked in a previous post if you tried running some good quality paper and your response was that you tried OTHER paper. The problem of the sheet delaminating tells me one of 2 things.... Either the stock your running is total crap, or your inks are too tacky. Actually it could be a combination of the both. If you've got no choice but to run job lot paper, then you need to choose a low tack ink set. Some people are of the belief that a high tack ink will give the best dot reproduction with the least amount of dot gain, and this is true. Successfully running these higher tack inks comes with the expectation that your printing on a decent quality sheet, with a printing surface that can hold up to the shear forces of the high tack ink. Some people don't even know what a decent quality sheet is. Im not trying to suggest that your one of them people, but you did come here looking for answers, and this is a possibility that you should look at. There is no shame in running job lot paper, if your business model and customer expectations calls for it. It is, and always will be, about making money, and the allure of the lower cost of job lot stock is sometimes too great to pass up. Its at this point that you need to match the tool to the job. A low tack ink set will be your best bet if running such stock. You won't be able to print with the best dot fidelity but it just might help you with your delamitation and sticking to the blanket issues. You can always compensate for the lower tack inks dot gain by adjusting your pre press curves. If you choose to count yourself as a "quality" printer, and want to print with the lowest dot gain and the most dot fidelity, then I suggest you again match the tool to the job, and spring for a first quality sheet. A good test to prove out my theory, would be to purchase a carton of some first run stock in the same weight and finish, and try running it side by side with your problematic paper.
     
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  13. Andrei

    Andrei Member

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    Thank you for your time and answers, I will look in to this
     
  14. alibryan

    alibryan Senior Member

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    ‘Bottom of the barrel’ is a funny term. It’s usually used to reference the last (or leftover) part of something , therefore implying it to somehow be undesirable, or sub-standard. But that’s not always the case. For example; a coater supply line takes from the bottom of the barrel first, and then returns the unused portion of the coating to the top of the barrel. It’s an essential process in keeping the contents mixed from beginning to end, so all parts are equal.

    And no one’s ever heard of saving the best for last. That would be ridiculous.
     
  15. turbotom1052

    turbotom1052 Senior Member

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    The bottom of the barrel I refer to is the mill rejects from the mills nobody ever heard of. Im talking bout the stock that chunks off all over the blankets, or when sheet sizes from sheet to sheet vary close to an eight of an inch. Or the stuff the OP talks about where the coating delaminates and blisters as soon as you put any kind of coverage to it.
     
  16. mz000

    mz000 New Member

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    mostly it's the black ink tack,
     

  17. turbotom1052

    turbotom1052 Senior Member

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    In most 4 color process ink sets, the black is tacked the highest. What follows is cyan, magenta, and yellow, tack rated in descending order. If you reduce the tack of your black ink, you are in theory required to reduce the tack of all colors that follow. This would mean you would need to reduce all 4 inks to be able to print with optimum trap. It would be much easier, and less costly to just purchase a lower tack ink set. If the occasional job comes up that requires the tackier ink, just pull it off the shelf. It would require you inventory 2 sets of process inks but thats a small price to pay to be able to print correctly.
     
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