3D Printing Desiccating Filament under Vacuum

[jlabrasca]

I have a couple of spools of wet filament that will no longer print cleanly. Lots of popping and strings and blobs.

Looking at the available drying options, and and after getting a whiff of what came out of the lab oven when I tried to bake a spool of PLA, I decided to try putting them under vacuum for a few days.

I tried to fabricate a vacuum chamber from an old wort kettle, but I couldn't get it to pump down to less than -0.2 bar. After a few fruitless hours trying to track down the leak I decided that my time was worth more than the price of an eBay degassing chamber. I am pleasantly surprised at how well this thing holds vacuum. I don't imagine the silicone collar seal will hold up to too many cycles, but for right now it is working.

I threw in a couple of saturated-to-pink desiccant sachets so that I'd have something to look at for a clue if it is working, After 24 hours in the can, one or two of the sachets are looking distinctly mauve.

I don't know how much water is coming out of the filament, but it is definitely outgassing something. When I cracked the chamber this morning the smell was alarmingly strong.

Its pretty cold in the shop. and I can't think of an easy way to heat the filament while its under vacuum (The hotplate under the pot is really just for decoration).

I am going to leave it under vacuum for the weekend, see if I get improved prints on Monday.

 

[dhbarr]

They sell flat heating pads for this exact purpose. Garden heaters would also work, or maybe a chicken heat lamp pointed at the side.

 

[David Schwantz]

New to 3d printing.
Why is it so important to keep it dry? What will happen?

 

[Charles_McG]

New to 3d printing.
Why is it so important to keep it dry? What will happen?

Second sentence in the original post.

Stringing
Blobs
Lumps
Under extrusion
Poor bed adhesion
Poor layer adhesion
Popping/snapping noise

 

[jlabrasca]

They sell flat heating pads for this exact purpose. Garden heaters would also work, or maybe a chicken heat lamp pointed at the side.

Thought about a heating blanket wrapped around the can. What would be best, I think, would be a radiator inside the can and a chiller wrapped around the outside. Wonder how long you could run fish tank heater in a 70 torr ambient? >smile<

What I really want to do is bleed hot dry N2 into the chamber and pump it continuously through a cold trap.

What will happen?

Second sentence in the original post.

The plastic is hygroscopic. There is more to it, and you will find some absolutely bonkers explanations when you google "wet filament", but some of the most obvious effects are due to the water absorbed by the filament "boiling" (coward quotes because of physics) in the extruder. It screws up the rate at which the material is extruded. The filament flows out too fast, or doesn't flow at all.

 

[cwbullet]

New to 3d printing.
Why is it so important to keep it dry? What will happen?

Stringy prints, poor adhesion, under extrusion, jams. I an keep going but it depends on the filament and hydration level.

 

[jlabrasca]

Stringy prints, poor adhesion,

Check and check. First three layers are clean, then it started spitting and leaving strings. The last layer wasn't sticking to anything.



This was the spool from the middle of the stack of three that I had under vacuum for about 72 hours. The hot plate was on "warm" -- which my $18 Etekcity pyrometer called 58°C.

I was surprised that all of the spools in the stack were warm to the touch when I cracked the chamber. I wouldn't have expected a 60-70 ~100 torr ambient to do much to transmit the heat from the bottom of the chamber (even if the thermal conductivity of the plastic is higher than I'd have expected the bottom spool was held up by a couple of big glass marbles, so it wasn't in contact the bottom of the chamber).

The only desiccant sachets that turned fully blue were at the bottom of the chamber -- directly in contact with the heated floor of the pot. I will clean off the bed and run a test print from the bottom spool -- but I am disappointed that the first test failed so early. If even the outer wraps of the spool are still wet, then the turns adjacent to the windows in the spools are going to be wet all the way down.

I am going to try again, with just one spool in the chamber.

edit: If the pressure gauge was accurate I was at about -0.9 bar when I cracked the chamber. The pump was rated for -0.82 bar when it was new (in 2001). I am guessing the pressure in torr wasn't as low as the double digits.

 

[jlabrasca]

Well that didn't take long. This is the spool that was at the bottom of the stack -- closest to the hotplate.

Rather than go for the hat trick, I am going to clean up the printer and run a print with a dry spool, just to be sure that I am testing what I think I am testing (noticed some black gunk in that blue bird's nest -- the hot end is overdue for a scraping).

 

[Wallace]

Any luck?

 

[Yukon@K-9 Rocket Tech]

New to 3d printing.
Why is it so important to keep it dry? What will happen?

Think of it this way. If you have dough and you add water, it will become soft and not bake right. Simpliest way I can think of

 

[Wallace]

Although I have several options at hand for drying filament I've yet to try it. I do have a couple of spools that could stand some drying but they just get put in the "I'll get around to that later" pile. When I get to the point where I'm not sitting on 20ish+ full and partial spools I'm sure I will become more motivated

 

[Yukon@K-9 Rocket Tech]

I've had one spool that was wet before, but never had that issue again. Just put all the spools I had into a huge box and put a ton of desican into it

 

[jlabrasca]

Finally getting back to this.

Repeated the attempt with two rolls of filament, and the hot plate turned up to "medium" (about 72°C by the pyrometer). Its cooking the water out, but the vapor is condensing on the colder upper parts of the chamber. It is dripping from the fittings in the lid.

This is what I saw after about 12 hours under vacuum.



I cracked the chamber, wiped everything down, and sealed it up again. I put a piece of silvered paper (recovered liner from a Goldfish Crackers bag) on top to the uppermost roll, to protect it from drips.

I will open it and wipe it down again in the morning, swapping the positions of the rolls. I'll see how they print after 48 hours under vacuum.

I will put the wettest roll -- the roll of PLA that came with the printer -- in the chamber with a sheet of emergency blaket mylar and some absorbent material on top of it. I plan to mass the roll before it goes in, and after it comes out, to see how much water (and other volatiles) are cooked out.

 

[jlabrasca]

Nuts.

 

[Greg Furtman]

What size degassing chamber it that?

 

[jlabrasca]

What size degassing chamber it that?

10.5 liters -- 3 gallons, more or less.

 

[KBlack]

Most all filaments will absorb moisture with poor effect on print quality, especially PETG and Nylon, but it's good practice to just keep them all dry as moisture serves no benefit in the storage or printing of filaments.

I keep all my filaments in sealed bins accompanied by molecular sieves, 3A size.
example: https://www.amazon.com/HFS-Molecular-Sieve-Zeolite-8X12m/dp/B0791CD231/
Bins: https://www.amazon.com/gp/product/B00MWTJWXS/

Molecular sieves can dry much closer to 0% RH than silica gel desiccant packs.

I keep a RH meter in my filament boxes, you can use the electronic type, or these indicator cards are a cheap and reliable option. https://www.amazon.com/gp/product/B01974FX42/

When it needs a recharge, I put the molecular sieves in a pyrex baking pan, spread out into a thin layer, and microwave them until a little after water stops condensing on the pan walls(3-4 minutes, YMMV.) Then if I want to be very thorough, I'll let them cool down in the vacuum chamber under vacuum, but it's not required for great results.

I also keep some molecular sieves in the sealed cereal storage container (https://www.amazon.com/gp/product/B00BEUDWIC/) that I put the filament I am printing with. The roll sits on a filament spool roller (with skate bearings) and the filament feeds out of the container through a PTFE tube to the printer. (Photo attached.)

 

[Greg Furtman]

Most all filaments will absorb moisture with poor effect on print quality, especially PETG and Nylon, but it's good practice to just keep them all dry as moisture serves no benefit in the storage or printing of filaments.

I keep all my filaments in sealed bins accompanied by molecular sieves, 3A size.
example: https://www.amazon.com/HFS-Molecular-Sieve-Zeolite-8X12m/dp/B0791CD231/
Bins: https://www.amazon.com/gp/product/B00MWTJWXS/

Molecular sieves can dry much closer to 0% RH than silica gel desiccant packs.

I keep a RH meter in my filament boxes, you can use the electronic type, or these indicator cards are a cheap and reliable option. https://www.amazon.com/gp/product/B01974FX42/

When it needs a recharge, I put the molecular sieves in a pyrex baking pan, spread out into a thin layer, and microwave them until a little after water stops condensing on the pan walls(3-4 minutes, YMMV.) Then if I want to be very thorough, I'll let them cool down in the vacuum chamber under vacuum, but it's not required for great results.

I also keep some molecular sieves in the sealed cereal storage container (https://www.amazon.com/gp/product/B00BEUDWIC/) that I put the filament I am printing with. The roll sits on a filament spool roller (with skate bearings) and the filament feeds out of the container through a PTFE tube to the printer. (Photo attached.)

@KBlack What size (cups I guess) cereal storage container is that?

 

[beeblebrox]

@KBlack What size (cups I guess) cereal storage container is that?

Walmart has plastic storage containers that easily hold four rolls, with air tight gaskets.

AND MADE IN USA!!!!!!!!!!!!!!!! Not in China.

 

[thequick]

In the chem lab we use a desiccant like Dry-rite in the vacuum chamber to trap the water vapor. Similar to what Kblack described.

 

[Charles_McG]

Way back when I did a moisture assay for Quaker Oats, the vacuum oven had a small bleed. It wasn’t static - there a was little flow to carry the volatiles out - controlled with a needle valve. You want the incoming air to be dry. 3A does a fine job. At the time, we bubbled it through concentrated sulfuric acid.

 

[jlabrasca]

Way back when I did a moisture assay for Quaker Oats, the vacuum oven had a small bleed. It wasn’t static - there a was little flow to carry the volatiles out - controlled with a needle valve. You want the incoming air to be dry. 3A does a fine job. At the time, we bubbled it through concentrated sulfuric acid.

Yeah, I thought about that.

What I really want to do is bleed hot dry N2 into the chamber and pump it continuously through a cold trap.

 

[KBlack]

@KBlack What size (cups I guess) cereal storage container is that?

It's a 21 cup Rubbermaid container.
Here's another link where you can buy it: https://www.everythingrubbermaidstore.com/store/1840750!HPD/