Magenta Ink Variaton on Web Offset

[nilay]

Friends,

From last couple of months we are seeing Magenta ink varaition on different units of the multiple presses: sometime high ink sometime low ink. Below is the detail.
Press: Goss Colorliner cold set web offset
Checked: changed ink packs, checked ink pump, checked blanket to plate impression, check rail setting, changed blankets, ink vendor checked ink: but still we are seeing same problem. Only one thing is left from my side: to place the ink can on the unit and engage the press to get ink from the same can: if it is good then we may have ink pumb problem. Please share any ideas or thoughts to find the root cause of the ink variation.

Thanks in advance for your help.

 

[Deleted member 16349]

Friends,

From last couple of months we are seeing Magenta ink varaition on different units of the multiple presses: sometime high ink sometime low ink. Below is the detail.
Press: Goss Colorliner cold set web offset
Checked: changed ink packs, checked ink pump, checked blanket to plate impression, check rail setting, changed blankets, ink vendor checked ink: but still we are seeing same problem. Only one thing is left from my side: to place the ink can on the unit and engage the press to get ink from the same can: if it is good then we may have ink pumb problem. Please share any ideas or thoughts to find the root cause of the ink variation.

Thanks in advance for your help.

Nilay, I think this is the first post on this forum from someone who is using ink packs on a press. This might make it harder to get an answer but it is also a very interesting problem.

Most here will not know what an ink pack is or a rail.

Can you be more specific about the variation problem.

Is the variation going up and down or just going one way and then needing correction?

Is it mostly in low coverage jobs or on any coverage?

What inking system (supplier) do you have for the ink packs etc. ?

Should I assume you are pumping the magenta from a central ink room with a supply pump to all the magenta press units. Is it that pump you are talking about when you talk about having a ink pail at the unit? I am assuming this is low viscosity ink and I am guessing you would be attempting to feed the ink to the ink packs at the unit. You maybe should check to see if those packs need some ink positive pressure to work properly.

 

[Deleted member 16349]

Nilay, I hope when you solve your magenta variation problem, you will kindly comment on how the ink packs system on your press compares to conventional open ink fountain presses with respect to density control.

Thanks.

 

[nilay]

Erik,

Ink pack is the device fixed on each page postion on the unit. See below detail

Ink pack: it gets the ink from ink measurement software and provide ink for each column as needed. So in general ink controlling device on the press
Rail: will get the ink from ink pack for each column and transfer to the VSI (oscillating) and pickup roller. Finally ink will go to the blanket by multiple ink rollers and foam rollers.
Magenta ink variation: ink is sometime high or low in terms of density, visual appearance. If you set the ink of the page with proof: you will notice change in magenta ink visually and also by densitometer. Variation is happening on the whole page or whole unit: so blanket to plate allignment will be the last factor to check. Which we already did.
Ink Packs are from the Goss
It happened on all coverage of ink: so not on low coverage: in low coverage sometime we purged the ink and set it as required near to the proof.