Heid PM72 Banding

[Colin]

Im having a problem with banding on my 72. It mostly happens on screens usually when running full colour presentation folders. The band appears in the same spot on every sheet, about half way up, and in the same postion on both units(2 colour press). I have tried taking back form rollers one at at time with no change. I have tried differnt water settigns and adjustments. I cant see it being our CTP because it doesnt happen on every job. I have checked my packing and it is the correct thickness.
What else could it be?
Colin

 

[Paultheprinter]

Hi there,

stop the press with sheets running through and note the point at which the sheet is released from the impression cylinder grippers to the transfer drum. If they line up with the band then its blanket release/transfer issue, my guess is that this point is further down the sheet (roughly 3/4 of the way down)but need to rule it out as you say its identical on two units. Are both units set the same in respect to lateral oscillation point ? if they are move it and see if the band moves, ive had bands cause by unwanted movement in the forms and its an easy cure, try these and repost and im sure we all will sort it.

Paul

 

[flyby54]

Hi
Have you tried printing the job on a different stock?
Sometimes it is just a combination of coating and acid or alkali content of the paper!

Paul

 

[Colin]

Thanks for the replies. Still trying to fix the problem, but its tough when you cant put jobs on hold. Quick fix was to take off more impression than usual and that seems to work ok. I am going to try the differnent stock option which would make for an easy fix. I dont think its hitting on transfer because there are no smudged dots.
Thanks again for your help and I'll repost in a few days.
Colin

 

[madjock]

This is the classic Heidelberg bump and it is caused when the blanket drops into the gap on the impression cylinders, on older presses you can see a polished mark on the bearers which would line up with where the band is, one way round it is to feather your packing or cut it in a subtle "V" shape on the back edge of the blanket, this causes the off impression thud to be less severe and should help with the banding, although in my experience it doesn't work on card stock.

 

[Colin]

one solution

one solution

The only thing we found that worked was taking back the impression enough to loose the band without compromising the job. The dot is still there and only the eye of a pressman could see a difference.
Thanks for your help.
Colin