Stripes printing on Web Offset

[jsnkiefer]

Hello all,
We are having a problem with our Web printing. We get striping on the lead edge. I'm in prepress and trying to help.
Pressmen are telling me they can't get rid of it. One pressman thinks it's from the rollers bouncing when it hits the plate gap. Another thinks it's from cheap ink.

Has anyone seen something like this or ,maybe, can offer any suggestions?

 

[Joe Duffy]

Is it on all units or just 1?
Is it new or has it been around for awhile?
What type of press? - web offset covers alot of presses and different issues.

These will start to get you answers

 

[jsnkiefer]

Is it on all units or just 1?
Is it new or has it been around for awhile?
What type of press? - web offset covers alot of presses and different issues.

These will start to get you answers

It is on all units. It has been around for awhile, sometimes it's worse than others. It's a Goss Community.

Thanks, Joe. Like I said, I'm in prepress so if I use the wrong terminology or if you need any more info please let me know.

 

[Joe Duffy]

I have not gotten roller bounce on Community - if the stripes and pressures had been set right. I hope they checked this before they came into prepress.
How old are the rollers on the press and are they in good condition?
To rule out prepress, have them hang a set of plates upside down and see if the bounce is still at the top - bet it is and that means they have to find the issue in the press.
Could be rollers, pressure, bearing related. Doubt it is cheap ink because how come it is only at the top?

 

[jsnkiefer]

I have not gotten roller bounce on Community - if the stripes and pressures had been set right. I hope they checked this before they came into prepress.
How old are the rollers on the press and are they in good condition?
To rule out prepress, have them hang a set of plates upside down and see if the bounce is still at the top - bet it is and that means they have to find the issue in the press.
Could be rollers, pressure, bearing related. Doubt it is cheap ink because how come it is only at the top?

They are not blaming pre-press. I am trying to take the initiative and try to find an answer to their problem because they are just shrugging their shoulders and saying "we don't know". Not good enough for me.

It's definitely a press issue. They are telling me rollers, blankets, fountain solution are in spec. It's always on the lead edge, if that helps with diagnosing.

 

[Dan Roll]

Check the packing of the plates and blankets, if they are packed to different overall diameters, this type of streaking can be one of the results. Do the pressmen complain of tail cracking as well?

 

[jsnkiefer]

Check the packing of the plates and blankets, if they are packed to different overall diameters, this type of streaking can be one of the results. Do the pressmen complain of tail cracking as well?

Thanks, Dan.
No tail cracking. The plate cylinders are made for the thickness of plate we're using (no packing) and the blanket packing, rollers, and blankets are all new and to spec, I'm told.

 

[Dan Roll]

What are the specs the plates and blankets are packed too?

 

[jsnkiefer]

What are the specs the plates and blankets are packed too?

From our GM: "The plate cylinders were manufactured to run a .008 thick plate with no packing. The blanket cylinders require .085” total blanket plus packing. All units"

 

[Dan Roll]

Well, now I would ask;

What is the undercut on the plate cylinder?
What is the undercut on the blanket cylinder?
Are you running .008 plates?
What is the total of the blanket thickness and packing?

Just because the book that came with the press says to do something a certain way does not mean you should do it. Goss has, over the years, dispensed some pretty bad packing requirements.

 

[Alois Senefelder]

Stripes !!

Stripes !!

Hello jsnKiefer,


What you are seeing are - Cyiinder Gear Marks - these marks are related to the Cyl Gears Teeth Pitch Circles

To eliminate this problem - the Blanket/Plate Cylinders Pressures need to be Reset by a Qualified Press Engineer !


Regards, Alois

 

[jsnkiefer]

Well, now I would ask;

What is the undercut on the plate cylinder?
What is the undercut on the blanket cylinder?
Are you running .008 plates?
What is the total of the blanket thickness and packing?

Just because the book that came with the press says to do something a certain way does not mean you should do it. Goss has, over the years, dispensed some pretty bad packing requirements.

Thanks, Dan.

From our GM: Plate is .008” undercut. Blankets undercut .081”. Yes we are running .008” plates. Blankets are packed to .084” total blanket plus packing.

 

[Joe Duffy]

Well, now I would ask;

What is the undercut on the plate cylinder?
What is the undercut on the blanket cylinder?
Are you running .008 plates?
What is the total of the blanket thickness and packing?

Just because the book that came with the press says to do something a certain way does not mean you should do it. Goss has, over the years, dispensed some pretty bad packing requirements.

And if it has been moved or cylinders redone, newspapers typicall would run a .0065 plate plate to save money, could be your .008 plate is thicker than what it undersut for. Also, what is the true thickness of the plate, are you sure they are .008?

 

[EGWebguy]

Sorry, I think it is a pre-press issue, but not of your own doing. We had this exact issue a number of years ago on our Timson
T32 and we found out is was bad plates. From the manufacturer. We washed the plate and using a loupe found that the coating was coming off the plates either during processing or after our fountain solution was applied. Try ordering different plates or a different manufacturer of the plates.

 

[BeauchampT]

If it is all the units displaying this problem, it has to be a universal variable - you can pretty much rule out things such as roller settings, etc. (unlikely that they are all set equally poorly).

Ink also is a little less likely (usually cheap ink will vary in quality colour to colour). That said, have you changed ink recently? If you have, use a lithographic window test to see if it is a tight tolerance - it might be a poor ink/water window is allowing some other weaknesses of the press to show up....

I would lean towards fountain solution or plates - even if things are up to spec, doesn't mean something hasn't changed. Are you a multipress facility?? Has anyone on anther press seen same problem???

 

[Rickyo]

I would clean water system trays ,check socks rollers ,settings first then see what you got