double image

Discussion in 'Komori Printing Presses' started by USAPressmen.com, Nov 2, 2009.

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  1. USAPressmen.com

    USAPressmen.com Senior Member

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    I was running my 1987 K 626 today, printing a booklet multiple pages up on a 100 text 19x25 - run this all the time.. After about 2000 or so sheets, the text in the position closest to the tail on the operator's side was getting a slight double image on the black text. Seemed like every other sheet... even on the other forms, always in the same position. I originally though it had to do with the feed board wheels - made adjustments - no difference, no bouncing. Continued to run job with double imaging since this particular job was a low quality job anyways- they will never know, it wasnt that bad at all.

    After i started backing up, i noticed my 6th unit that i had off, seemed to have a lot of ink on the blanket from previous forms that day. Infact, i had to clean it because it was transfering onto the paper as if I had left the impression on, but the impression wasn't on. After cleaning it, it would eventually come back to where I would have to do it again... I did run that unit earlier in the day but washed it up and turned it off after i was done.

    After I left, i began wondering if my original double image problem was a result of the 6th unit blanket or if it was just a coincedence. If it is, the why - loose blanket perhaps? Could it be stuck on impression but not have the impression light turn on as sheets start to go through the press?

    Im sure its just something stupid that I will probably be embarassed about later lol.
     
  2. RichardK

    RichardK Senior Member

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    Every other sheet sounds like a gripper out of setting or a cam follower breaking up.

    Next time you get the issue drop 6th into pressure and see if the double improves. If it does, it may be that the sheet is 'kissing' the blanket as you run.

    It may help, depending on ink coverage, to run your Black last.

    Heresy!? :eek:

    Not at all... we do it when there's a 'black only' tint that we want to print clean and if there's minimal chance of poor ink lift/trap. You may have to reduce the tack of the black to overcome this.

    You don't say whether other colours 'double'. Are you perhaps running too much black on the op side?

    We run an L626 and find it good practice to clean the non-printing blakets at the same time as the ones in use.
     
  3. KGM

    KGM Senior Member

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    Had the same problem last year, always on lighter stock. gripper service sorted it out (my engineer did it). also try using a wire brush to clean the gripper pads.
     
  4. KOMORI DEMONSTRATOR

    KOMORI DEMONSTRATOR KOMORI DEMONSTRATOR

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    Hi, from what you have said a straight in and then out double points to a gripper problem 99.9% of the time.A gripper service will sort out your problems.
    Although as usual all Richards points are valid.
     
  5. USAPressmen.com

    USAPressmen.com Senior Member

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    thanks guys for all your posts.. I havent run into the problem again (yet), but im curious to know if its only happening on text stock - i've been running nothing but cover stock since the problem. I'll be sure to check the grippers next.
     
  6. 5150pressman

    5150pressman Senior Member

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    Do you change your gripper pad height when you go to print board stock and forgot to change it back??
     
  7. RichardK

    RichardK Senior Member

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    If it is a case of the thinner sheet hitting the blanket you could try running with the blanket off.
     
  8. USAPressmen.com

    USAPressmen.com Senior Member

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    Im starting to think its the gripper now.. I just ran a 11.5 x 17.5 cover stock job with no issue and then had problems with a 12.5 x 19 text stock. Every 5th sheet or so would come into the delivery crooked and cause a jam up. Sheet would go into the press fine, but must be getting screwed up somewhere between the 6th unit grippers or delivery grippers.. I'm making this assumption because the sheet is printed on ( not folded over or half printed ), just majorly crooked as it comes into the delivery. I couldnt run the job on 80# text, I had to switch to 100# text and run the press really slow.
     
  9. RichardK

    RichardK Senior Member

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    Check where your sheet is positioned in relation to your grippers. You say a change of sheet size and stock weight gives you this issue then make sure the sheet is not only just held by a very small amount at the leftmost or rightmost edge.

    check where the sheet is gripped on impression and transfer cylinders - make sure it's well into the leftmost and rightmost grippers - anything less than 3mm is gonna give you a potential problem as you describe.

    Every 5 or 6 sheets? Maybe one set of delivery grippers are not quite set right and just missing the tip of the sheet and then you get the fouling.


    Happy weekend ;)
     
  10. rolandman

    rolandman Senior Member

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    every 5 or 6 sheets would suggest in my mind its a delivery gripper issue however if you check if the sheet has been printed straight (witht the tick marks), if not its probs at the infeed...
     
  11. USAPressmen.com

    USAPressmen.com Senior Member

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    yeah sheets are printing straight... Sheet is getting good infeed gripper on left and right side.
     
  12. RichardK

    RichardK Senior Member

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    Just another idea...is the sheet long or short grain?
     
  13. rolandman

    rolandman Senior Member

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    Have you checked the Delivery Grippers to see if anoy of them are loose?
     
  14. RichardK

    RichardK Senior Member

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    Or just out of set...they fairly easy to reset. Let me know if you need instructions.
     
  15. USAPressmen.com

    USAPressmen.com Senior Member

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    I will be checking them on monday :)

    Tried both grain directions with same result.

    Although I haven't looked at the actual grippers that closely, I assume they are just like most other presses - use 60# text weight paper and test how tight each single gripper is. I suppose there should be a allen wrench adjustment screw on there?
     
  16. RichardK

    RichardK Senior Member

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    Not so much testing for tighness as for timing of transfer opening/grip/release of the sheet.

    I'd check by running sheets out of pressure, stop the press when sheets arrive at unit 6 then lift cover over 6th unit to delivery and inch sheets until you checked for clean transfer to all delivery gripper sets.

    To adjust (and do check your manual first as presses may differ) you need to insert a feeler gauge (in our case L626 it's .05mm) under the rightmost stop and then lift each gripper in turn insert a thin sheet of stock, undo the rear part of the gripper and simply press the gripper onto the stock/gripper pad and retighten. Repeat for each gripper and each gripper shaft in turn. It helps to mark the first bar with a strip of tape so you don't accidentally adjust a bar more than once. ;)

    Repeat the plain paper run to recheck the transfer of sheets into tthe delivery grippers.

    You didn't say whether you're getting creased sheets prior to transfer into the delivery.
     

  17. Loupeyeyed

    Loupeyeyed Senior Member

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    These are two completely different problems. First off, you will never get a double image from your delivery/carrier bars. Shame that you have two things going on at once though. Makes me wonder how often the press is greased and maintained. Your double image on text weight could be coming from a few different places. Are you impression cylinders clean where it is doubling? Are you over packed or not changing bearer pressure between cover and text? And first and foremost are your impression cylinder gripper functioning and set properly?
     
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