Packing question?

Ok our blanket cylinder(s) is .096 undercut, our blankets are .076 4ply. To achieve bearer height would I use .020 under blanket? our plate cylinder(s) are undercut to
.011 and we poly pac at .004 with a plate thickness of .012 to get us to .005 over bearer height..sound correct? press is a mitsubishi d3000. Just asking because the press people there before me are packing the blankets at .024 We are printing and I have noticed a slur on some stocks in black unit on gear side. And at the tail on some larger sheet 4 color jobs the black/cyan are shorter to achieve register than the magenta and yellow? is that due to the over packing of the blanket(s). We have also had some trouble with piling in black unit here and there. These all seem like overpacking problems to me....am I getting somthing wrong?

 

are you measuring your blankets and packings or are you just reading whats stamped on them? ive found that there is often a difference between what the blankets and packings say they are and what they actually mic. out to be!!! An even better way would be to check it all with a packing gauge. I feel its a worth while investment even if your shop has just a single multicolor press. I like to run a 4 ply compressable blanket with a total of .004" to .005" total squeeze.

 

Well got a TRUPAK and the blanket is even with bearer. thanks turbotom for the feedback...Im also glad to see that specs call for .005 over plate bearer and that is on the nuts also..gota love that TRUPAK!! now i'll just have to go into k unit and clean grippers.

 

ive seen cases where manufacturers specs need to be deviated from a bit. cylinder circumfrence has been known to vary from the factory. also at times a press needs to print at the same lenghth of other presses that are allready on the floor up and running. My feeling is that although it would be nice to be able to run to manufacturers specs, whats more important is that a press fits from unit to unit and how we arrive at our total plate to blanket squeeze is not as important as maintaining the proper squeeze! If a plate needs to run a little over or under the bearer in order to print at the correct lenghth then it can be made up under the blanket. of course it goes without saying that im talking about deviations of no more than a couple of thousandths of an inch. the scales on the press can always be adjusted even if digital.

 

hi..turbotom..i would like to know what is blanket squeeze?
as i am new to this field i am not able to understand some technical terms...will you please explain??

 

"blanket squeeze" is the contact patch between the mounted plate and the mounted blanket at the nip of the 2 cylinders.

 

really thank you for the explanations...
you have insisted to pack the plate under the blanket for little over or under bearer...
if plate is packed over the plate what will happen..??

 

i have a doubt turbotom1052....
in cpc machiines which of the following is best..kba or Heidelberg??
sir i would like to know ur mail id..??

 

vg you can reach me through the private message feature on this forum

 

eagle1, turbotom suggested that you use a packing gauge. I have to agree - in fact, I think that using a packing gauge is an absolute must. Don't ever forget that even though you are using a blanket that is made to be .076", it loses one or two thousandths just by tightening down the blanket on the cylinder. I recommend that you use a torque wrench to tighten the blanket down so you can always tighten it down the exact same tightness, and also that you use a packing gauge to see how low/high your blankets and plates are. If you can't afford a proper packing gauge, make on out of a piece of U-channel and a good Starrett dial indicator.

 

VGB,
adding packing under the plate will make the image print shorter from gripper to tail. subtracting packing from under the plate will in effect allow the plate to wrap around the cylinder more to make the image print longer.
It should be noted that if you add .003" to under the plate you need to subtract .003" from under the blanket in order to maintain the required squeeze between the 2 cylinders. now that youve subtracted .003" from under the blanket you need to adjust your back cylinder pressure that same .003" in the direction of more pressure in order to compensate for the decrease in blanket packing. its just the opposite if your looking to print longer.