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Swissengineer

Printing PVA = Lots of problems...

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Hello everyone,

I would like to share some experiences I've had with PVA printing.

Since I got my brand new UM3E, I use really often PVA for small supports, because it is easy to remove (lower adhesion, and I don't even need to put in water! That's cool!)

That means I use it every day. So I can't remove the spool every time to store inside a bag.

So I'm guessing my PVA is absorbing water and then being more fragile (more grinding)

And the result is bad insertion and non constant material extrusion.

Here is some pictures to illustrate.

5a33245bc0b50_20161201_0835301.thumb.jpg.0d8a4f2f85eb9685a54dc3bf46e50d3b.jpg

5a33241a431c9_20161125_1329571.thumb.jpg.6688f00258a671fe6198ad84394b44a1.jpg

Do you guys have any solutions? or had the same problems?

Btw, I've tried lowering the tension, I did a cleanup of BB core, my PVA spool is only two weeks old...

5a33245bc0b50_20161201_0835301.thumb.jpg.0d8a4f2f85eb9685a54dc3bf46e50d3b.jpg

5a33241a431c9_20161125_1329571.thumb.jpg.6688f00258a671fe6198ad84394b44a1.jpg

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Nice! I think the scaffold is PVA based, so I guess I can try the same thing!

To bad ultimaker doesn't make a cover for PVA spool

 

Scaffold is indeed PVA-based so warming your PVA on a bed should hopefully work for you. I also believe that Tom Sanladerer bakes his filament to dry it, which should work as long as the temperature is VERY low.

It's genuinely quite a challenge to keep PVA dry enough to print reliably though (hence E3D's vacuum-sealing and desiccant), as moisture doesn't just mess up the filament melt, but also dissolves PVA and messes with its chemical structure.

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You can heat it in an oven but you have to stay below the softening temp of PVA.  I measured this but lost my notes so I'll have to measure it again some day.  But I was surprised at how it softens at a very low temperature similar to PLA.  I remember it was within 10C the same as PLA but I forget if it was higher or lower.  PLA softens around 55C.  I strongly doubt PVA is that low so it's probably around 60C.  But could be 50C.  Anyway I would set my oven temp to 60C and leave it in there for many hours.  When drying filament out that can handle 100C (boiling temp for water) it dries out very fast.  But 60C is going to take much longer!

Don't use a gas oven as that produces a lot of moisture and I'm guessing it won't dry as well in a gas oven (not certain - maybe it somehow works anyway?).

Edited by Guest

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Thanks guys I thought I would have to put everything in the trash! I will try all that,

I have a climatic chamber so I can control the humidity level.

I hope the spool holder doesn't melt!

To solve all that I'm thinking about designing a new spool holder inspired of your designs. But I need mine to be as small as possible. Like the one for scaffold but with a solid enclosure like the one from ultiarjan. As soon as I have it I will do some pictures!

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You can put your PVA spool on the heated bed at 55 degC for a few hours. That will drive out the moisture.

If you use the PVA in a climate of RH<55%, then it stays in good shape. Above that, the chance of jams becomes higher, because the PVA becomes soft. Temperature has the same effect by the way, stay under 30 degrees.

Don't trust the dial of your oven at such low temperatures, as it is probably not accurate. You may ruin your spool.

Is your hotend in good shape? If you have had an incident where the hotend was hot when there was no flow (jam, end of roll, ...) the PVA will have transformed into a brown sugarlike substance that (partly) blocks your nozzle.

see this page on the Ultimaker website to unclog your nozzle. Don't be afraid to use multiple hot-pulls before trying a cold pull.

Edited by Guest

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What you could also do, is keep the spool of filament locked in a sealed bag with disseccant (if I spell that correctly). And only take it out to unwind and cut off the required amount of filament. Then immediately put the spool sealed away again. And only feed the cut off end into the printer. The disadvantage is that you need to calculate some spare in, and the piece of filament in the bowden tube is always lost. You you have a lot of waste pieces of filament. But this might cost you less than destroyed models, especially in a commercial environment. I am not a fan of wasting material, but in this way the total waste may be less than if you have too many failed models.

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I use 1 spool per box. Just place it next to the machine. I don't care about the automatic rfid spool reading....

Picture is 1 spool nylon. 1 spool pva.

Material feeds through a short piece of bowden.

Screenshot_20161207-233323.thumb.jpg.b381b73374f025c655ba49f35b3b79fa.jpg

Feed left box into right feeder.

Screenshot_20161207-233323.thumb.jpg.b381b73374f025c655ba49f35b3b79fa.jpg

Edited by Guest
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Hi Folks,

This is really an interesting topic, however I’m just a “mono 3D” printing individual, so I do not need this setup yet, but who knows..  But I’ve been thinking about such a dry house for the filament, in order to leave the filament on the printer.

However, I’ll always store the filament into a sealed box allowing two rolls of filament to be stored into here. I’ve also put a bag of Calcium chloride (450 gram) together with a wireless humidity/temperature sensor. As I’ve a light version “weather station” allowing to use of up to four sensors of this kind, this extra sensors went into those boxes. :)

Here’s a picture of the inside of the box:

Storagebox_inside.thumb.jpg.ea4373dfd415235fb6f5b51279fc53fd.jpg

Here is it with the cover on and some spec. information on top:

Storagebox_outside.thumb.jpg.ad11566cce2e26a445543fc418744beb.jpg

This is the link to my source for this type of box:  

http://www.clasohlson.com/se/F%C3%B6rvaringsbox-SmartStore-Dry/Pr341515031

And here is the source for Calcium chloride:

http://www.biltema.no/no/Hjem/Rengjoring-og-vask/Utstyr/Fuktsluker-2000019534/

At least those links might be handy for the Scandinavian audience. :)

Thanks.

Torgeir.

Storagebox_inside.thumb.jpg.ea4373dfd415235fb6f5b51279fc53fd.jpg

Storagebox_outside.thumb.jpg.ad11566cce2e26a445543fc418744beb.jpg

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I think we got way off topic. The original poster *might* have a problem with humidity but most likely, not. There are other causes for ground up filament. Similar to those of normal filament that gets ground up. If you print the material too fast and too cold then it slips or if you have so many retractions that the same piece of filament is retracted 10 times (the same exact spot of filament goes back and forth 10X before getting through). Or 100 times.

Or maybe your tension is too loose. Or too tight. Although I have to say tension looks about perfect.

Hmm. Most likely you have a partial clog and the printer is having trouble getting PVA through the nozzle. Maybe it's time to do the cold/warm pull as recommended for PVA clogs by ultimaker.

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Hi gr5,

I'll see you point here and agree. But i don't think we're that much off topics, cause this PVA is alcohol based and does attract water very fast. Then become hard and brittle, moreover the memorized spring effect is increased.

So, when you're a little down on the roll, the filament will try to keep its memorized radius and then start making S - pattern inside the bowden without being compressed.

I'll think this is the reason for this focus.

Just my 5p.

Thanks.

Torgeir.

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Wow Lots of replies! Thanks!

After a few tests I can confirm that my problem was humidity in the PVA filament.

I took a new spool then printed correctly.

If you read my first post at the end: The first thing I did was clean the heads with cold and hot pull.

Okay back on PVA,what I'm guessing based on my experience of 2 weeks printing everyday with PVA is:

When PVA is exposed to humidity. It becomes more "breakable", so harder.

If you take for example a cookie left too long in the oven, it will not be squishy but will crack very easily.

Now talking a little bit more scientific:

5a3324cce76f2_Typicalstrainstressbehavior.JPG.2f214acce23089d57819025617e29d0e.JPG

ss-curve-metallic-wire.png.3ffb006f573301a3cf0f104670c73f8e.png

For us we always need to stay in the elastic behavior for the insertion of the material be good.

So our best solution is what ultiarjan and others did. Keep the materials (All of then them) is a low humidity box.

I'm still a bit surprised, ultimaker did not propose an idea, maybe they did not have the time to.

As soon as a make my solution I will post for you guys! But it will wait next year!

5a3324cce76f2_Typicalstrainstressbehavior.JPG.2f214acce23089d57819025617e29d0e.JPG

ss-curve-metallic-wire.png.3ffb006f573301a3cf0f104670c73f8e.png

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I didn't know that PVA gets more hard or less flexible or more brittle when wet.  That's very interesting!  I think this is a good test for my stress/strain tester machine!

 

Thats very much true, even with my setup with PVA in a container, the PVA gets super brittle when left in the bowden, so I need to unload the materail after use.

When I start using it I just check the end by bending it (if it breaks its bad) I sometimes have to cut off like the first 30 cm because it's gone brittle...

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Experience in Ultimaker R&D is that PVA stays fine for months when humidity stays in "normal office conditions". Let's say 20-25degC, up to 55% RH. This holds for Ultimaker PVA, other PVA's we have tested are much more sensitive to moisture!

Here in the Netherlands in summer, sometimes humidity goes above 55%, and temperatures sometimes rise to 30degC or even hotter. The reliability of printing PVA then drops to unacceptable levels: too many prints fail. Cause for failures is that the filament gets too soft for the feeder.

The statement that PVA gets brittle with moisture is opposite to our experience. Both temperature and moisture make PVA soft.

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To be clear I have no problems with ultimaker pva. It prints easy and reliable. That said the first 30cm orso did go bad on me multiple times while the rest of the spool is fine. So I have no idea what else would cause this than humidity. Im in the Netherlands and room temperature is normal. No means to check humidity but I see no reason why it would be abnormal.

For me it's no issue at all to check the start of the spool. Waist is very limited.

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Fascinating. Well @ultiarjan the same symptom is true of the newer formulations of Ultimaker PLA. If you leave it in the bowden for 8 hours it becomes very brittle! And it has nothing to do with moisture but has to do with mechanically straightening the filament and holding it in that position for many hours.

I really don't know why it does this. I'm guessing you get micro-fractures occurring slowly over many hours. Or maybe something down at the chemical bond level? What REALLY surprises me is that this same thing happens with non-PLA. I did *not* expect this to happen with PVA.

I have not experience brittle PVA yet. I was always nervous about humidity so after every print I have always put it back in a bag with dessicant.

I have a stress/strain machine that I built myself and gives me stress/strain curves just like the ones shown above. Some day I plan to print up several PVA test parts and then expose them to different levels of humidity/water for different amounts of time and then test them on the machine to see what the curve looks like.

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