horizontal streaks in web offset newspaper printing

[Kaizen]

Hi all,
We are observing the consistent problem in newspaper offset printing. Horizontal streaks in solid colors. Observed
them on Plate cylinder too.
Need your expert opinions for possible reasons or causes.
Thanks..

 

[Dan Roll]

If by horizontal you mean across, rather than around, the cylinders, I would check to see if the diameter of the printing surfaces (plates and blankets) are roughly equal (if the cylinders are the same diameter and in correct proportion if they are not). Streaks that are perfectly parallel and across the cylinder are usually caused by a discrepancy of the surface speeds caused by incorrect heights of the printing surfaces.

 

[Bagfoot]

Whenever streaks show up, go back to basics first. Make sure roller settings are correct, make sure they are the correct durometer, check the impression is correct and throws on solid, make sure your packed correctly and everything is tight, then check for a bearing problem.

 

[Kaizen]

Dear Mr. Dan,
Yes they are across the page and more visible in dense areas.

Thank you very much for your guidance.

Thanks to Bagfoot too, for your input. Will look in to it.

 

[Dan Roll]

If your press used to print without streaking I would investigate any changes since then affecting the height of the blanket and/or plate surface and try to go back to whatever set-up you were using before. Changes in plate or blanket thickness are a common cause of this problem, as is attempting to eliminate packing under one surface by raising the other.