Need Help Black creating lawnmower lines

[sgxJeff]

I'm having an issue when printing jobs that have black. Everything starts out fine, then when there's a period when black is not in use, then its starts back when needed, its creating the lawnmower pattern. We have replaced the dampers and capping station, still does the same thing. We even swapped out the ink to a brand new one, still the same. I linked pictures to show what I mean. Thanks for your help!

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[MikePro]

culprit is in the test print. missing nozzles = bad print.
try soaking the head overnight and see if you regain any, otherwise you may be looking at a printhead replacement.

 

[sgxJeff]

Did a test print and looks all clear. Then we ran a job, and it started the pattern again with black.

 

[dale911]

When you say test print, do you mean nozzle check? Obviously in your second photo, it's clear you have clogged nozzles which is causing your "lawnmower lines" which is actually referred to as banding. If you search for banding, you will find a wealth of knowledge.

Now if your nozzle check is clear and you begin printing and you lose nozzles and it starts banding, it can be a variety of issues. You mentioned dampers and capping station so I will assume this is a solvent printer, likely Roland, mutoh or Mimaki? You need to figure out why you are losing the nozzles. Are you using 3rd party ink? How long is the printer sitting before you try to run the black? What settings are you printing with? My solvent printer runs great almost 100% of the time but my latex machine will begin banding and sometimes lose a an entire head if I run a huge area of the same color, primarily black or magenta. I have found that pushing a lot of ink through the machine at high speed causes ink starvation on my ho l25500 so the solution is the increase the number of passes or usually, I set a pause between passes so that the ink supply has time to maintain its fill of the head. Good luck!


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[GaSouthpaw]

You undoubtedly are missing some nozzles. Once that's fixed, may I suggest making sure you're not printing 100% black, but a "rich" black instead (I forget the exact values)?

 

[MikePro]

Did a test print and looks all clear. Then we ran a job, and it started the pattern again with black.

that test print doesn't look clear at all. lol
if you're nozzles aren't firing at 95%+, you're screwed. yours are at like 30% on the K channel.

if that is how your test print looks at the start of the day/print, you shouldn't even try printing. clean and/or replace printhead
if your test print fires at 100% and then it starts printing wonky and then new test print shows like your photo, then you have an ink supply issue.... either being improper contact with capping station, bad ink pump, cracked manifold on printhead, bad damper, or airbubbles in ink lines.....basically could be anything. between the ink cartridge and the waste tank. ...isolate, narrow-down potential sources of error, diagnose, & fix. or get a service tech in.