problems with damp solution

[Gav1n]

hi there am new to to this.im currently working on a heidelberg 5 colour gto printmaster.we've had the press since august and in this time have had problems with our damp.the main problem is a light band of tint that appears in the middle of the sheet after about 3000 sheets.im pulling my hair out with it!were using ctp plates,i was using supreme fount to the percentages of 2 and 4% and isopropyl alcohol at about 10%.the problem started so with the advice of our local supplier we changed to ctp sheetfed fount both founts supplied by varn.its supposed to help keep the alcohol at a minimum,it helped slightly but the problem is still happening?!a guy is coming in this week to do a conductivity reading,but im just wondering if anybody else has had this problem because its a new 1 on me.could it be possibly be the plates?any help would be appreciated.thanks Gav.

 

[Paultheprinter]

hi there,

sorry to send you in this direction but i doubt its your fount, i run sm74s and heidelbergs and ive found most lines across the plate cylinder are caused by mechanical problems not chemical. Try marking the banket cylinder where the line appears, check to see if theres any toning in this area. Open the drive side hatch and move the reciprication an inch or too and see if the line moves, i will be very suprised if it stays in the same place.

please repost Paul

 

[rbailleu]

ahh dds damps bite someone else in the rear. I bet it starts at about 7 inches down. thats where dds runs out of water. tones the rest of the sheet. try setting your water temp colder. add more alcohol. reset rollers.

 

[Gav1n]

i think your right with this dds!have you ran with the dds before and if so did you have this problem.what percentage was your alcohol?i tried marking the blanket cylinder but no joy.i've had a conductivity meter reading today,every thing was fine and the temp is also o.k?i've ran 74's and cd's but have never seen this before?this direct damping has been a bit of a nightmare from the off!thanks for the input guys.but any 1 has worked the dds before it would be great to get any info.
thanks Gav

 

[Paultheprinter]

when you marked your blanket did you change the resiprication point? i assume you did and this did not help which would send me down th direction of either the point that the damping soloution is inherently flawed which is no help to you or your suffering from strap lines from where the sheet is transfered from the impression to the transfer cylinder which could be solved by quick release blankets (buffed) or a harder blanket, try inching the sheet to the point on the blanket where the line is and see if it is at the point the sheet is transfered.

Paul

 

[rbailleu]

could be a gripper transfer issue, but I bet what is happening is that at about 7 inches the system is toning/ starving for water. the only thing that fixed this for us was lighten all the setting for roller to roller to about 2-3 mm the settings for water rollers are critical. our gto was a 1996, one of the first for dds. heidelberg completely replaced the dds in our system 2 years later. this helped alot, but never solved our issue. and then change the system in subsequent models. we finally just went to a sm52.
I can't for the life of me understand why they just did not stick with alcolor. yes It cost an extra 2000 per unit. but it works. its simple. people understand it. it did not require re-enginering. 4 rollers not seven. but I am sure they had a reason.