PVA Extrusion Issues

[tgwertz 0]

Situation: I loaded Ultimaker PVA Natural through print core BB.4. It started flowing smoothly, but it never flowed straight from the nozzle, it always had a slight curl to it as soon as it extruded. I was a little concerned, but it was brand new straight from the box provided, so I didn't think too much of it. I started my first print with the PVA and noticed it was barely adhering to the bed (magigoo applied beforehand and a heated glass bed of 60C for the Tough PLA I was using through print core 1). Upon further examination, the PVA coming out of the print core was wrapping around the nozzle. I aborted the print. I had some issues getting the PVA to unload. After finally getting it out, I decided to re-load the PVA and run it through longer, thinking it might clean out the nozzle (if that was the issue). It never flowed straight and kept curling upwards (worse than before). I unloaded the material, it removed easier this time, however, it looked like the image below, long thin section near the tip and an area that seems to have been ground down by the knurled loading wheel. 

 

Note: The PVA has been in a dry box for 3 days, and sitting at a 10% humidity and 23 C. It was put in there as soon as I opened the bag it came in. It is also set up to pull from the box as it prints. I was using the pre-loaded settings in Cura for the PVA.

 

Question: What is the issue, tension on the loading wheel, nozzle/print core needs to be cleaned, or something else? What's the best way to fix this?

[gr5 2,224]

While curling *can* be an indication that the nozzle is slightly clogged - it isn't really a big concern.  I usually ignore that.

 

MUCH more likely the problem is with leveling.  Make sure the tip of the nozzle is clean when you run active leveling.  Watch the procedure.  Make sure the timing is the same when it first ever checks the right and then left core.  It should go down extremely slowly, touch the bed, move down just a tiny bit more and pop up.  If it pushes the bed down for an entire second or if it doesn't quite touch the bed before it pops up - then it's a leveling issue.

 

However to clean a BB core you should really try a "cold pull".  The maintenance menu will guide you on this.

[gr5 2,224]

Just to explain better.  If there is 0.2mm of pva on the tip of the nozzle when you do active leveling and if it isn't melted enough or if it has been hardened through "baking" and is a brown hard substance, then as soon as that pva on the tip touches the bed and the bed starts moving down - then active leveling will level your nozzle such that it will print too high and the pva will just curl and never stick to the bed.

[tgwertz 0]

Thanks, buying cleaning filament and then doing a cold pull seemed to fix the issue.

[tgwertz 0]

The first print after performing a cold pull worked alright. It didn't seem to 'cut' the PVA cleanly when switching between print heads, but it was acceptable. The second print, it was doing the same, didn't think much of it, but I woke up to find the PVA support had broken off and there was strands of PVA throughout the rest of the print. What is the issue here, is the print head too hot, faulty print head, or possibly something else?

[Carla_Birch 116]

PVA is a fussy filament to get working right, if you don't need to be able to remove support from with inside a print due to not being able to get to it, then i would personally try breakaway for support (going by if its a supported filament for the main filament you using)

 

As for PVA i would personally make sure you have a prime tower turned on under dual extrusion settings and you might also want to up the PVA temps a little if you find it dont seem to be flowing right (can also be due to wet filament, PVA loves to suck water out the air).

[tgwertz 0]

Thanks, I'll try the prime tower and upping the temperature, then I'll update with the results. It's definitely not a humidity issue, it's being pulled through a Polybox at 10% and the print environment is ~30%.

[gr5 2,224]

Most likely the PVA isn't dry enough.  It only takes a few days in normal room air conditions (50-60% humidity) to make the PVA "worse".  It's easy to fix.  Look how much PVA is used - it's shown in the bottom right corner near the "Slice" and "Save" button (example it looks like less than a meter for your print).  Then unspool at least that much PVA and place it directly on the heated bed with the spool on top (so you don't have to cut the filament).  Then cover with a towel or other good insulator that will let moisture through.  Then heat to 60C (careful as if you go to hot you will melt/deform the PVA) and let it sit like that for a few hours.  Afterwards you are ready to print.  If you don't unspool it can take a few days on the heated bed to dry the whole spool out.  Much faster to just unspool a few meters.

 

Then when done printing don't leave the PVA on the printer.  Immediately put it in a sealed 2 gallon zip lock with a cup of dessicant.  Use color changing dessicant and you will see that it needs recharging (heating in microwave is easiest) every few months.

 

Nylon is just as bad.  It's a wonderful material but Nylon and PVA need to be kept very very dry.  You don't have to do any of this with PLA (I don't even keep dessicant with my PLA).

[lancy 0]

My UM3 printer nozzle head is clean, PVA material is very dry and we have a dry box while printing.  After 2 to 3 hours of print, the PVA material didnt extrude well from the nozzle, so the loading wheel keeps rotating, rub the PVA portion and the extruding stops.  This happens every time. The loading wheel tension is factory default, nozzle is cleaned, PVA is dry. After 2 -3 hours, the extrusion slowly cease. How can we fix this ? I am using 0.4 mm nozzle. A higher size 0.8mm nozzle solve this problem ? ultimaker PVA default temperature is 215c.

Edited October 19, 2021 by lancy

[gr5 2,224]

Using a BB 0.8 is indeed a good idea but you shouldn't have to do this.  Also if you have a BB 0.8 you will end up using a lot more (expensive) PVA.  And if you work for a large company you probably don't care and this could be a good solution.

 

Or you could try a brand new BB 0.4.  The problem you describe could be cause by so many things!  For example something in the feeder side of things or something in the print core end of things.

 

I never trust people who say their filament is dry.  Do you have a humidity sensor?  You want I think 10% to dry it and 20-30% to keep it dry.  Those numbers are almost made up - they are from not-so-good memory and things I've read from taulman and ultimaker.  But I think they are probably correct numbers.

 

If you have a box with dessicant in it - how much dessicant?  You really need a LOT of dessicant.  LIke 100 of those packs that come with the filament.  I use about 1 cup of color changing dessicant and I can see the color change when it's time to recharge the dessicant.

 

You could be right - it's completely dry filament.  But please give more details as this is really the most common issue.

 

CONSTRICTED CORE

 

Okay - other issues - the BB core gets a layer of caramelized PVA in it after a while.  You have to do about 10 or 20 cold pulls (and do sme hot pulls also).  You can characterize things by using the MOVE command and seeing how long it takes for a kink in the filament (use your fingers to create one) get all the way down to the print bed.  Count that in seconds.  I want to say 10 seconds is probably pretty damn good but I never write the numbers down and have never done the test with PVA (only other materials).  This won't tell you much this time but will tell you a lot next time you have a problem.

 

PRINT HEAD FAN

 

What you describe is exactly what happens when you have a bad print head fan - not the 2 side fans - but the fan in the door of the printer.  Check to make sure it's spinning or you can feel airflow (suction) going into the head.

 

NOZZLE TOO HOT

 

PVA gets caramelized very easy at normal printing temps.  If you mess with the settings in cura (if you raise the nozzle temp for pva) you are also likely to get this exact symptom.  You could try lowering the temp by 5C (in the TUNE menu live while printing).  This may instead make it fail earlier if the issue is "constricted core" above.  And if you messed with the temp before today - put it back to defaults.

 

[gr5 2,224]

Quote

My UM3 printer nozzle head is clean,

Also note that it's the *inside* of the nozzle that we care about.  You can't see that. You can just try to do a LOT of cold pulls.

[gr5 2,224]

I hope you read my other two posts above.

 

I reread your first post.  That "curl" is indeed a little concerning.  I have a hypodermic needle which is great - very sharp cylinder cut at a steep angle.  Much better than a normal non-hollow needle which doesn't have sharp edges.

 

Anyway I have a 0.35mm hypodermic needle and I use that sometimes to scrape the inside of the nozzle.  Followed by a cold pull.  I do the scraping as it's in the cool down stage for the cold pull and try to push those scrapings up into the nozzle for removal by cold pull.  This can help restore a nozzle with a layer of toasted/black filament baked onto the inner surfaces.