CET white ink questions.

[synergy_jim]

I'm not real sure what to make of that. Negative pressure suggests vacuum which would hold ink in the head. If you turn it to a higher negative value, you would think for vacuum so less ink flow. My reasoning was to turn it to a lower vacuum IE -3.2 to see if the ink would flow and cure the nozzle dropout...

 

[artbot]

the negative pressure is just like holding your finger at the top of a straw and then drawing it out of the fluid. it will hold the fluid by vacuum. by lightly lifting your finger away from the edge of the straw a small amount of fluid will escape. adjusting the negative pressure (odd use for the word "pressure" because we think of pressure as only being positive) lower the ink will fall out of the heads more easily. and then of course raising the temperature will lower the viscosity of the ink just like heating up an oil or anything else that is viscous.

 

[synergy_jim]

the negative pressure is just like holding your finger at the top of a straw and then drawing it out of the fluid. it will hold the fluid by vacuum. by lightly lifting your finger away from the edge of the straw a small amount of fluid will escape. adjusting the negative pressure (odd use for the word "pressure" because we think of pressure as only being positive) lower the ink will fall out of the heads more easily. and then of course raising the temperature will lower the viscosity of the ink just like heating up an oil or anything else that is viscous.

Great! my assumptions were correct. I laid some white paper under the heads last night to see if the low pressure was allowing the heads to seep. I saw very little. Tonight, when we shut down, we moved the pressure back up to -4 to see if that will stop the little bit of seepage we saw last night

 

[Nameci]

Since pigments on the whites are heavier than the other colors, you need to find for the right compromise. Also take into account the air leakages on the system. The thing that holds the ink is not the vacuum per se but the force induced by the vacuum. To maintain the required force to hold the ink, the vacuum is directly proportional to the contact area which is the total area of the nozzles and the area of the air leakages.

 

[synergy_jim]

periodic loss of magenta ink today for no reason. cleaned the head, rebooted system and printer. Came back... any feedback on that?

 

[artbot]

my white ink is reborn!

i took the day off. only to get back the shop with white ink acting up. not intermittently but every three to five feet it would drop.

i've noticed that the white heads just can't reach 49. even if i set them to 52 (the max), they won't get to but 47.6. so i theorized that the lm lc heads were
probably the least worked heads in the carriage. we (my very talented machine operator) resorted the config file so that white ink would be at the lm lc and vice versa then ran the lines criss cross.

now i've got some piping hot white ink heads. i can run them up to 52! (and did). negative pressure was at 2.7.

i've never see so much ink fall out of those heads ever. i had to back off my usual white in setting to 50% to get the density the same as usual. i was getting a pure flood of
white at 45% in my spot channel.

so if anyone is having white ink choppiness, just rotate the tires. plus consider that the white heads are the hottest heads in the whole carriage. they really should be rotated to get
more life out of them. also at night i have a special "at rest" config that lets the carriage cool down. then i just swap configs in the morning and i'm hot again but i still have the pumps and
such running without all the needless heating.

 

[artbot]

along with this CET/white ink discussion. i'd like to here what heat setting is common for the color. i looked at our settings and all the color is set to 40. that seems really cool. please chime in on this one because we are still really green with the machine and a tiny bit of advice can save us months of aggrevation.

thanks!

aa

 

[Rob Bellissimo]

so if anyone is having white ink choppiness, just rotate the tires. plus consider that the white heads are the hottest heads in the whole carriage. they really should be rotated to get
more life out of them. also at night i have a special "at rest" config that lets the carriage cool down. then i just swap configs in the morning and i'm hot again but i still have the pumps and
such running without all the needless heating.

ArtBot, i would love to hear more about this "at rest" configuration. can you send a screen shot of your settings? we run a CET Q series.
thanks

 

[artbot]

it's quite a simple set up. save your current calibrated config file. save that file and title it "config print". now go back to your settings and drop all of your temperatures to something far less toasty and click "write". now save that config file to the same folder.

keeping both of these two config files in a separate folder one titled "config print" the other titled "config rest". now put the config/firmware file and these two saved versions of the config as shortcuts on your desktop. you can now quickly manage two temp settings. when you are done with the printer for a good while (overnight to several days) go straight to the config file and delete the config file. then copy and paste the "config rest" file to the firmware folder. right click and rename it "config" now go back to your print module in your rip and go to temperature and click "write". the new cool settings will drop all of your temps at once. of course to get back to print reverse this. delete config (which is the rest settings), copy and paste the config print, rename it config and click write in your temps. we have strings of days when we are proposing and designing that we don't print at all and it's so much better to know you aren't cooking those heads for days. but, still have misting and the white ink recirculation going.

 

[Rob Bellissimo]

it's quite a simple set up. save your current calibrated config file. save that file and title it "config print". now go back to your settings and drop all of your temperatures to something far less toasty and click "write". now save that config file to the same folder.

keeping both of these two config files in a separate folder one titled "config print" the other titled "config rest". now put the config/firmware file and these two saved versions of the config as shortcuts on your desktop. you can now quickly manage two temp settings. when you are done with the printer for a good while (overnight to several days) go straight to the config file and delete the config file. then copy and paste the "config rest" file to the firmware folder. right click and rename it "config" now go back to your print module in your rip and go to temperature and click "write". the new cool settings will drop all of your temps at once. of course to get back to print reverse this. delete config (which is the rest settings), copy and paste the config print, rename it config and click write in your temps. we have strings of days when we are proposing and designing that we don't print at all and it's so much better to know you aren't cooking those heads for days. but, still have misting and the white ink recirculation going.

Thank you! we will try this... :Big Laugh

 

[synergy_jim]

FYI....... I'm printing t-shirts on my CET now...... I think I may sell this jig after I patent it.....

works like a charm!!!!

 

[jonharrell]

White ink help??

We have just recently got a new CET flatbed and the printer has been working great except for the white ink. We have not had any luck on getting a good looking nozzle test from it. Do you have any suggestions for me? Attached is nozzle test picture and controller. We have flushed the head and it looks fine when flushing. I'm just don't know were to go from here. Thanks.

 

[artbot]

one is you can flush with NMP instead of CET cleaner to do a really great job of cleaning the nozzles. of course, in this thread there's the discussion of using lower pressure which i'm sure you've tried. if you are having issues with white and don't want to mess up prints, you can do a couple preventive things on the file prep side. when we were having white ink issues, we would put a 1/2" strip of white to print first before the file began as a spot. this would give us fair warning if we were good to go on the print. you can do the same on the left or right side or both to keep it primed. in my experience, if you don't have an issue starting out, the white will flow fine.

also, it hasn't been mentioned but shaking your white container is very important. the resin/pigment will separate and it needs to be aggressively agitated. ...very aggressively. don't swirl it. shake the crap out of it. getting the mix to completely blend is important. if unblended you can be eventually printing (or attempting to) print a white that has a higher ratio of pigment thus a higher viscosity.

 

[Nameci]

Artbot is right. Looking at the images of your printhead nozzle test I can see that your heads are Ricoh's. I am not sure as well about the latest ink chemistry that CET Color is using, but first you have flush your heads to make sure that the nozzles are not clogged. I would suggest that after flushing with NMP or CET Color flushing solution, you have to push air using a syringe thru the nozzle to fully drain the flushing solution from the head ink chambers.

Fill ink to heads and purge the air thru the extension tubes on the printheads, reprime the heads and wipe it clean.

Be very observant with your negative pressure. Again the property of the ink here comes in to play. White ink are usually heavier than the other colors because of the metallic pigment. Your negative pressure is called the meniscus vacuum on some other machines. Which is but only correct, because the ink is forming a meniscus on the surface of the nozzle plate. Too much of a negative pressure/meniscus vacuum, it will pull the ink towards the head and forming a deeper meniscus in which the piezo will no longer have a volume to eject. A low vacuum would cause the meniscus to bulge outwards and would cause the ink to stick on the nozzle plate because of surface tension.

Increasing the printhead temperature would cause the ink to decrease its viscosity thus also decreasing surface tension. It would be easier for the heads to jet the inks but the effect would be overs praying or satellites most especially if the carriage is moving at a faster speed.

There is usually a sweet spot and depending on your environment, it is not really hard to establish it.

Also once the heads are jetting white really well, maintain it by printing at least a foot square of full white image in order to eject the old ink that is on the heads. Remember that you might have ink recirculation on the primary tanks, but there is none on the ink, since the ink is heated on the heads the tendency of the pigment is to settle down on the bottom which is on your nozzles.

Therefore there are 3 parameters that you have to find for the sweet spot.
1. negative pressure
2. ink/printhead temperature
3. printhead voltage (This will be the last that I would touch)

It could only be an air bubble trapped on the heads if it was jetting well previously.

My two cents.

 

[synergy_jim]

sooooo......

So, we continued to have white head problems and eventually lost half the head. The tech came last week and replaced. Head printed good for 2 days. weekend comes..... monday starts dropping nozzles again....

Now the whole head is non functioning.

Anyone out there having issues???


We have the auto spray set up to spray 5 times every 100 seconds just like CET recommends. I'm at a loss for what the issue is...

 

[synergy_jim]

so... everything is running now... white problems gone...

apparently the main board was not controlling the heads correctly. when purging, the heads were not purging with enough power to keep them clean....

electrical gremlins rule.

 

[synergy_jim]

1 week later. No nozzle problems and no head drop out..... Looks like our problems may be solved..

 

[artbot]

good to hear. white, if run often in a flatbed can be a dependable color. i think white worked better in hour CET than color. maybe because we were getting those heads really hot and didn't require the fidelity that cmyk does. who knows. it flowed really well regardless.

 

[synergy_jim]

good to hear. white, if run often in a flatbed can be a dependable color. i think white worked better in hour CET than color. maybe because we were getting those heads really hot and didn't require the fidelity that cmyk does. who knows. it flowed really well regardless.

I think all of our colors are working better now... that main board must have had some serious issues....

 

[Kurt]

Having an issue with our CET Q1000 - We took out both white print heads to send out for cleaning. The next time we tried to run the printer, we wanted to print a color on a white background (using white coroplast). The printer lays down a yellow background! Not in the art file! We notice that the printer is set up for 5 colors and wonder if shutting off the white setting will fix the problem. However, we can't find the setting. Anyone have any thoughts?