hello out there ,my name is Ke ..i run a 640 perfecter press with a coater komori lithron.. and i cant seem to keep the tail of the sheet from tearing when i run over 12,000 ..does anyone have any ideas.. i've tried turning my under fans off adjusting my air bars over the back cylinders it works for a little while and then it comes back ..i need a little advice ..im sure a straight press wouldnt do this ..but it seems like it does it when it passes the perfecting unit

Hi Ke...
tell me is the tear around 2 inch from back edge on drive side or operators side and is it lateral ie parallel to grip edge? If so then it sounds very much like a whiplash effect, you need to look at the final transfer into the delivery chain set. Do you run a skeleton final cylinder? If so I believe it can be fitted with sheet supports. Straight presses from 426 and up can do this at speed on thin stock. It's rare that it happens on 40" presses tho'. best of luck R

It seems like from time to time that the sheet will tear on either side..It does seem like a whiplash effect but it appears to be on the turn cylinder not the coater unit ..7th we have guide wheels that support the sheet on the coater unit..The odd thing is i can run straight 4 color at the tail of the press and get no tear ..but when i run in the center of the press and crank it up to 12500-13000 it starts folding and tearing the edge of the sheet..i've tried turning the under fans off ..turning them on and adjusting them low or high and theres air bars in beteen the cyliners that i've adjusted as well ..i can hear it poppin from time to time i've heard that the pit builds up air down there and maybe causeing this ..i dont know the answere ..

The pit builds up air - I 'm a tad sceptical - turbulence I could believe.
I suppose you could try covering the pit with some heavy boards to discount that theory. Have you tried printing short grain material? The popping is an indication that the tailedge of the sheet is collapsing then being stretched by the change of direction - it still sounds like the whiplash effect tearing the sheet.

This may sound silly but try slowing the press down until the tear is gone. If the tear is still present then you have a mechanical issue. Are you perfecting when you experience the tear? If you don't need the turning cylinder, then disengage it and run straight. If you are running book weight stock, minimize the air flow at all points. If there is a pattern to the frequency of the tear then you may have weak or broken springs inside the turning cylinder. I think you should have the springs checked out first to be sure they are good. Should those spring be damaged you will fight this issue until the Queen cleans her own pigeon coop. Good Luck. John.