landing mark??

hi guys,

we have run our cd 74 5 now for 9 months but are still having an issue with a mark we cannot get rid of,it seems like a landing mark in the delivery but we have tried everything and we cannot get rid,we have had a heidelberg uk demonstrator in for a full day and he could not get rid of it either,he seemed to think it was a landing mark and that the air in the delivery looked too harsh,we have tried to run with no air at all but it still is there,it does not seem to happen on paper above 200 gsm,we have had a heidelberg uk engineer in on a follow up to the demonstrator but again he could not solve it,he said all timings on the grippers were set correctly and the sheet release was also correct.the mark always seems to have a curved sort of shape,we have checked all basic things like if its picking up the mark through the press etc and of couse so did the demonstrator,the mark is normally in from the edges about 4 inches and is also about the same from front of sheet but is random in size and postion which sort of rules out the picking up through the press,the appearance looks very similar to the marks on our transfer jacket after the perfector but i dont think its this as it moves about,i know its not ink /water as we have tried lots of different inks including heildebergs own and we have had a chemist in to check water etc,we are runing to iso 12647 so again i know we are putting the correct amount of ink down,the press prints fantastic and the ink dries very quickly whilst in the stack,the machine does not have a coater and heidelberg have told me that they have not sold many like this but i cannot believe the they woukld make a machine that cannot deliver a sheet without marking,the delivery is the the new xl 75 type so for the life of me i cannot resolve this,any body seen anything o theirs and found a cure,
cheers for any help

 

http://i25.photobucket.com/albums/c96/peterh7036/mark.jpg
not really the best pic as this looks a bit like a thumb print

 

Looks like a landing mark caused when the sheet collapses between the sheet brakes in the delivery

 

hi,
yes it does look like that and the press operators reckon they can almost see the sheet collapsing and if they play with the downward air they can sort of get the creae to stop but not the landing mark,heidelberg demonstrator himself could not get this to stop either.they have talked about putting a nano meter on the air to make sure thepressure is correct,we have tried it with no air as i mentioned but it still dont really stop the issue..

 

It will be to do with the dynamic sheets brake, have you tried moving the position of the 2 outermost brakes?,
would be leaning more towards the first row of fans(closest to the feeder) if these are set too far forward they cause a ripple in the sheet because you tend to run them faster to compensate.
Another thing to ask it may seem a silly question but is the dryer set too high?

 

hi thanks for the offering,we dont have a drier or coater its just a 5 colour perfector.

 

You get that marking during straight and perfected jobs? The picture shown, is that the top side of the sheet?

 

Hi
The mark is always on the back of the sheet
In the pic it shows the mark it may have happened on side one or side 2
It's almost as if there is one jet of air more powerfully and
Bending the sheet causing a crease and then that "wet" crease
Is marking the next landed sheet
But proving it or stopping it we cannot do

 

Does the second line contradict the first?


It looks like a brown grease mark on my monitor
No build-up of grease and spray in delivery unit?

Have you printed plain paper and emergency stopped the press and checked the sheets to eliminate marking within the press?
Checked there isnt any stray sheet under the perfector?
Feeder drum cleaned?

 

I'm not familiar with that model of press but I have 2 thoughts. Being that it's a perfector I'm assuming you have double storage drums covered with super blue netting after the perfector-check the air bars that blow the sheet against the super blue and make sure the bar is indeed blowing against the super blues and not down between the cylinders-older models of presses had bars that rotated and during cleaning of transfers sometimes get moved-this will cause the sheet to get a buckled effect. You mentioned that marking doesn't occur over a certain weight, this may be a good place to start looking.
DATA raised a good point about sheets under the perfector and I would suggest looking under the entire press. You may have to crawl under and check the sheet guide plates under each unit and check for any pieces of paper possibly stuck in a guide plate. Another place I have seen paper get lost in perfectors is after the last unit and before the delivery-again it means crawling under the press and checking for sheets.

Good luck Peter.

 

Hi
The press is a late 2007 cd 74 so it's basically
An xl75 ,it does not have super blues as the sheets float
On air
Ours is a 1-4 perfector which we rarely use
Air between units etc was checked by the Heidelberg
Demonstrator etc
The only thing the engineer said is that the air pumps
Have been installed on wrong side of press as they are on operator side
And they may be causing a turbulence as they are sitting
Not too far from where the perfector is
We have inched so many sheets through press looking
For interference but found nowt....
Peter

 

hi
its defo not grease as its an ink mark,it looks exactly ike the marks you get on the tansfer jackets,but there is nothing on them that can put a round end to it and the mark moves about,
the mark can happen when you are printing side one,or side 2,it looks like the venturi sort of shape with a sory or round head and then fanning out but again heidelberg checked this and it dont seemt o be that as there is no ink buld up anywhere,its also not a wet sort of mark,i appreciate it must have been wet at some point but when we run a stack and find it,its dry at that point.as i said we/heidelberg dont think its anything basic such as paper stuck etc or a lump of ink built up,but never say never....

 

I would go for checking all the air drums under the cylinders especially the one you can see the edge of in between impression and transfer cylinder you say its a 4 back one do you use the the last unit for sealing the mark to me looks more likely to be coming from round there again check all the air drums under the last unit that they have not been bent slightly if they are to close to the cylinders the sheet can catch them

 

Hi PeterH, If you ran 500 sheets without impression would all the sheets be mark free?

 

yes they would,by this i am presuming that without impression there is no ink applied so no ink on the paper will mean no landing mark.??

 

Yes, that's what I mean-no ink, no mark. Do you see any marks on blank sheets?
Have you been able to resolve the problem? I have a few more thought if it is still existing.

 

ji,

yes problem is stil there im afraid,
had a reply from heidelberg tecnical who have seen samples and they think its defo some sort of landing mark(wo ho).
they have suggested we run press slow and bring air on slow etc,
they know that we recently paid best part of 1000 pound to have their demonstrator come down to try and do exactly that but he could not get rid of the mark.
so any more suggestions are more than welcome,when our operator adjusts the air he can almost see the bend/crase in the sheet move about but even with no air at all he can still deliver the sheet,

 

hi giys,

i have checked all suggestions so far but found nothing really,anybody can suggest anything else.?

 

I noticed on an earlier posting you said the marking on the picture could have happened on first or second pass. I think that it is very important for your pressman to know when it's occurring-ensure that the pressman(men) are checking the back of the sheet while running the first pass-they/he should be checking for drag marks or wheel marks anyway. On the picture, was there heavy coverage on the other side that contributed to that mark?
You mentioned that the mark looks like a venturi air shape, with press stopped have you turned on the air and turned all the venturi air settings down to zero and then access the delivery and feel if any venturi airs are still on? It's possible that you have a stuck valve which is not allowing any air adjustment.
Not being there means having to ask what may seem like silly questions. Are there any sheets resting on the fans above the pile? Is your decurler one that needs to shifted into place? If so, there is a cover plate that sits in the decurler opening when it's in a rest position.

 

Not applicable on the CD74