Heidelberg Gto Mottle from Blanket

[SAICPRINT]

I have a GTO 52 single color (1981) , having serious mottled looking prints, tried different stocks
of paper, blankets, inks, solvents, fountain solutions etc... I should also mention that I have another Heidelberg in the shop that uses same ink/chemistry and has no issues.
I noticed the blanket has the same mottled apperence as the press sheet, You can especially see
it when you wipe the blanket with cleaner and can see the uneven surface of the blanket.
Is there something mechanically I should be looking for?
I have the plate at + .0047 and the blanket at -.0019
The only thing I have replaced on the press was impression magnet, (pic included)
maybe needs adjustment?

 

[Adil]

Can you show me the print image?

 

[SAICPRINT]

Here are two pics one is black at 50% tint fm screening
next one is cmy fm screening.

 

[mantman]

Have you changed impression jacket?
Also impression dial indicator is according to spec?
Put a 0.3mm feeler -or is it 0.35mm?- between blanket and impression ring with impression on and dial at 0.
It should have tight drag else they are out of sync and need to be calibrated.

 

[SAICPRINT]

I haven't changed the impression jacket,
With dial indicator on 0 I get a slight drag with .35mm feel gauge, not tight...

 

[Adil]

There are several causes for this problem
- support having different absorption behaviors
- pressure setting too low
- poor coating or tension of the blanket
I offer solutions as follows
- use an alternative medium
- support having a slower absorption
- increase the pressure settings
- replace the covering sheets according to the hollow of the blanket cylinder and ensure proper tension of the blanket
Good luck

 

[turbotom1052]

Ive learned not to trust the gauges or digital pressure readings until Ive been able to verify their accuracy for myself. The numbers are just that (numbers). Unless the press is a brand new installation ,where the numbers are known to be accurate and untouched, I would not trust them. My suggestion would be to fine tune all pressure settings on all units, with a fairly new blanket to the undercut specs stamped on the factory engraved plate. I would shoot for a plate to blanket squeeze of .004" with a relatively new compressible blanket, to be arrived at with a hand held packing gauge measuring at various points around the cylinders being checked. Once Ive established plate to blanket squeeze, I would do break away solids (without water) to get KISS impression for the substrate thickness. Once I was able to get a full impression across and around the entire sheet I would then calibrate either my mechanical gauges, or the potentiometers to match the sheet thickness. It should also be noted that even properly calibrated gauges and pots will be just a starting point when it comes to uncoated sheets. It is very likely that you will have to add a significant amount of impression cylinder pressure to print solid on uncoated stocks. You may even find yourself maxing out on the squeeze, and still not be able to print a full impression when it comes to lightweight uncoated stocks. If that winds up being the case then you will need to go back to square one, and rethink your plate to blanket packings. In a perfect world we would all love to be able to print to factory specs under all conditions, but Ive found it rare that it works out like that.