Four colour process registration on a single colour GTO 46 on cheap absorbant paper

Discussion in 'Heidelberg Printing Presses' started by emet, Dec 30, 2016.

  1. emet

    emet Member

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    Anyone got any advice for me about running 4 colour process on my GTO 46 on very cheap copy paper.
    My problem is registration. I can keep the colours in register at the front of the sheet (pretty much) but by the time I get to the back the paper seems to have swelled and there is no way to perfectly register. I had this problem on a newspaper web press but it was consistent the length of the sheet (or web) so we just adjusted the width plates ( in the front end) on different colours so they lined up. I would consider that here but it is pretty inconsistent.
     
  2. mantman

    mantman Senior Member

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    That could be extra pressure from impression or feeding issue -paper not steady when side guide pushes so use sheet brushes and sheet brakes-
     
  3. emet

    emet Member

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    From what I can tell the paper seems really steady on the feed. Also the error is very consistent. When I lay the film that I made the plates with over the printed image there is a discrepancy in dimension, not so much position.
    I do wonder about the pressure fromt he impression. When I got the press I got a new blanket and underblanket. I put a piece of .1mm packing with 1mm underblanket and 1.95 blanket. From what the manual said I was slightly more packed than should be. The manual said .06 packing. however my image was poor so I packed it .1mm more and it was good. This did not really compute with the figures for the undercut of the blanket and plate cylinders. Is there any way to put the cylinders on and off impression to make a stripe so I can check this?
     
  4. goldenpress_bahadurgarh

    goldenpress_bahadurgarh Member

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    Cut off the ink, put the damp rollers on a blank plate and pass the paper to let it swell.
    Then start printing from second pass onwards.
    Hopefully it should be helpful.
     
  5. mantman

    mantman Senior Member

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    There is a switch O.S that throws on impression to hang plates, as for impression print a solid breakaway to check condition of jacket or your blanket is not tight enough, so get yourself a torque bar.
    As far i remember by the book for figures:
    plate undercut 0.03mm, plate 0.15 (0,15-0.03=0,12) 0.12mm over bearer
    blanket undercut 3mm, blanket 1.95mm packing 1mm (3-1.95+1=0.05) 0.05 under bearer
    Squeeze plate/blanket is 0.07mm (0.12-0.05=0.07)
    Impression dial: paper thickness minus 0.05 under bearer minus 0.10 pressure=impression dial (eg 0.10 paper-0.05 blanket under bearer-0.10 pressure=+0.05 towards impression cylinder)
     
  6. emet

    emet Member

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    Mantman, I don't think that switch is on the GTO 46. Do you or anyone else know another way?
     
  7. junker1984

    junker1984 Senior Member

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    You really can't "stripe check" the cylinders. I would suggest doing a breakaway dry solid, though. This would tell you whether or not you're dealing with cylinder damage.
     
  8. turbotom1052

    turbotom1052 Senior Member

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    My first suggestion would be to be certain that your pressures between both the plate and blanket, and between the blanket and sheet is correct. Dont take it for granted that the blankets are what the manufacturer stamps on the back. Dont take for granted that the packings are labeled correctly. The best way to insure proper pressure is the check the printing heights with a packing gauge. Once you've established proper printing heights then it would be advisable to print with minimum back cylinder pressure to improve proper ink transfer to the sheet. DONT assume that the pressure adjustment gauges on your pressure settings are correct.
    Also be sure you are running long grain paper. If after checking all of the above ,and sure its correct if the problem persists you could adjust print length as needed to fit. Search the forum for threads on adjusting print length.
     

  9. Travis Young

    Travis Young Member

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    Hi Emet,
    I know this is an old post so hopefully it's long resolved.
    Old 46s don't have the switch for the impression that Mantman is referring to. You just lift a guard, pull the normal handle around to impression (as in run, dampening, paper, impression) and hand crank the press until it goes 'click'. Then the impression is on.
    You don't need to perform the above procedure to do a dry run but it's handy to know how to put the press on impression without it running.
    You are suffering from paper stretch.
    Just run a dry pass to stretch the paper before you start printing.
    Leave the dampeners out, lock the forme rollers off by pulling the forme roller handle out and sticking a bar through the little hole (not that it matters if there's no ink on the press) and pretend you're printing.
    Don't leave the ink duct screwed up tight when you're running dry as it might scratch the steel duct roller. And don't run for thousands of runs with no ink on the rollers, it will stuff them.
    Alternatively, if your job has tight rego on one side but not the other, do the easy side first. Your copy paper will be well and truly flattened before you start doing anything tight.
     
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