controlling dotgain

[cjwworld]

Thats great news.. at least maybe someone else might have the same issue and your solution might help

 

[dimitri]

just don't tell the press guys... they will start blaming the plates any chance they got

 

[Deleted member 16349]

problem solved

10% gain difference was caused by a plate developing unit.
we changed the developer circulator pump, as it stalled from time to time.

Ronson,

Glad the problem is solved.

Can you clarify some issues. In your first post you said that the dots on the plate were the same, but I am assuming the developer problem affected dots.

Once you found the developer problem, could you see that the dots on the plates were not as similar as you initially thought? Was the difference in dots measureable?

Just curious. Thanks.

 

[ronson]

It seems that I missed those plates where the difference was biggest.
We had to get digital microscope for accurate reading, handheld Gretag was off by (+ -) 4%

And cyan dot gain issue was completely ink`s fault.
This 5% extra gain magically disappeared when I added ink manually from new container.

 

[Deleted member 16349]

It seems that I missed those plates where the difference was biggest.
We had to get digital microscope for accurate reading, handheld Gretag was off by (+ -) 4%

And cyan dot gain issue was completely ink`s fault.
This 5% extra gain magically disappeared when I added ink manually from new container.

Wow. Very interesting. Problems where there are several things not quite right are the hardest to solve.
Good work.

 

[couriergraphics]

web tension, blanket stretch make sure they are tightening them

 

[Dr Who]

Dotgain that deviates this much always has a reason, if it is purely mechanical then it would usually show on an individual unit rather than every unit.

questions to consider
Are the dot shapes the same for both jobs ?
Has the SID increased/decreased as dotgain changes?
Has the paper type changed [surface coating]?
Have you changed anything? [new batch of ink etc]
Quality control bar problems?
Densitometer problems? [calibration etc]

If all units show large increase or decrease it is likely to be a process change [SID, Paper, Ink, dot shape etc]
If it is a single unit then it is likely to be mechanical or blanket loss of guage

Hi to all,

been looking for web offset related forum for a long time
I have some strange problems on my press.

On our press it looks like the dot gain has a mind of its own, one day the gain on 50% area is 15%, next day the gain on the same area and the same paper is 25%. (similar job)
Ink roller temp.(77F) and dampening temp.(52F) don't deviate very much.
Dots on the plates are always the same.

What are the most important things to look for when controlling dot gain?

Running Goss M600 4 unit press with Sun Chemical universal inks.

Thanks in advance.