Stories of engineers / Unstable operation of print heads.
Unstable operation of print heads.
I would like to share my experience on how to maintain solvent and UV printers. I am going to add advice, which I frequently use for diagnostics, revelation of breakages and maintenance of machines. They are neither unique, nor compulsory, but they will promptly help you to reveal a cause of a problem and will help to save time on the call for an engineer.
Below, I'll enumerate a list of general breakages and possible variants to solve the problems:
Unstable image printing, stripes are visible, colors disappear.
Firstly, you have to make sure what the problem is. There are main 3 variants:
1) Bad ink
2) Unstable vacuum system, no leaktightness in the ink track
3) Clogged print head
4) Too high speed of printing
5) Problems with electronics
And, first 3 problems have a higher probability, than the other 2. Then we start to define, precisely, which one of them has an effect on the operation of our machinery:
Firstly, we have to understand, with which color we have a problem.
We can easily check it by printing out a checkbar.
For example, we have problems with Magenta.
Then we do the nozzles test, and by condition of nozzles we define condition of print heads. All the nozzles have to prink fast and even, without any dust, gaps or unfinished lines.
Pic. 1. An example of a good test.
Each printer has its own test of the print heads, but concept is the same, to make sure in correctness of print heads operation.
Pic. 2. An example of a bad test.
1) Check density and reliability of pipes, which go to head, subtank, filter, dempfter.
2) On the sole of the head, drops cannot gather and dust cannot form.
3) If while cleaning-up the head by positive pressure, we notice emerging bubbles, then air inleakage is definitely happening, move to the 1 point.
4) Check reliability of air pipes
5) Check the correctness of air pomp; it has to work regularly, without big differential of rotation. There shouldn't be any creak, whistle, gritting.
6) If there is an acicular valve for vacuum regulation, then you should try to open or close it, to change the pomp rotation. It is possible that rotation of the vacuum pomp is too big or too small.
7) Check if there is any leaking on the subtanks and on the pipes which come up to it.
8) If this is a printer without the system of the vacuum regulation by vacuum pomp, than it is advisable to regulate presence of meniscus on heads, with the help of the subtanks levels, relatively to heads.
9) If this is an UV printer, that temperature of ink in the print head plays an important role. If necessary, you can try to increase or decrease temperature on the heads.
10) If dempfer is used on the heads, then you should check a respectability of its junction with the head. As dempfer is also a filter, there is a point in changing it more frequent.
Checking all this points and carrying out all this recommendations we exclude an impact of air, and all the other outside factors, which have an impact on stability of printing.
If we are certain of the vacuum stability, that there is no ink leakage, temperature and tension on heads are normal, drops don't accumulate on heads, and then it is advisable to try to pour the ink into those subtanks, which (ink) was printing well in the other head. For example, the color blue. Ipso facto, we will understand, whether it is the ink to blame for stability. If so, you have to immediately change the ink. It is common, that bad, sub-quality ink can hard print heads. Clog nozzles, block inner filter inside the head.
Also, you should not forget about the regimes of printing. It happen sometimes that because of the fast speed of printing, heads do not cope with the flow of ink and start to gulp with air. IF while decreasing linear speed of the carriage and decreasing printing expansion, stability of printing was managed to achieve. Then you should pay attention not only to the quality of ink but to the condition of print heads as well.
If you changed the ink and didn't achieve a positive result, checked vacuum system and vacuum is stable, then it seems to be a problem with a print head. Therefore it's time to clean up or change print heads.
If after replacement of ink, checkup of ink and air track, after cleaning and changing print heads situation doesn't seem to improve, it's time to check electronics:
1) Check all the laps; there might be a so-called tinkling of contact.
2) Sometimes, laps can bend
3) Black dust fall out on the printed-circuit board, which starts to close the contacts, leakage of streams happens. It all has a bad impact on the machinery.
4) Replacement of boards, power modules.
In my practice, unstable operation of the print heads happened several times, for the Konica Minolta 14 pl printer. We installed a control board of heads from Konica Minolta 42 pl.
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