A Vacuum Oven is the recommended Industrial Industry Standard by Stratasys, and Vision Miner as well. This is that, so you are using the most efficient method to dry filament.
The 2nd Part is when transporting & storage before printing (vac sealed bags, or sealed containers with silica).
The 3rd part is printing, and the AMS does well, adding silica and circulated heating helps as well.
This is like the topic of VOC from FDM, Resin (don’t forget the skin contact), CNC & Laser cutting ( don’t forget eye protection). No one really bothers to ask and research what the Industrial 3D printers do.
How much vacuum is the recommended industry practice?
I received this laboratory vacuum last week and haven’t even unboxed it yet, but it was for this very purpose: https://a.co/d/a2Gm8Xq
According to its specs, it can draw a limit of 0.085Mpa, which isn’t nothing, but neither is it the strongest one can buy. If industry practice is a harder vacuum, I might swap it for one of those.
It seemed like a useful bit of kit, because it can also generate a compressed air stream on a continuous duty cycle. And, importantly, it doesn’t rely on oil, which on the cheaper vacuum pumps can create quite a stink when running in vacuum mode.
On the other hand, if it were a super strong vacuum it might be hard to heat the filament, because then I’d be limited to heat radiated from the vessel walls. So, given the uncertainties, I elected for this as a starting point.
CNC Kitchen tried drying filament in a vacuum without heating, and it was only weakly effective.
Vacuum drying should work well but be careful. If you pull a perfect vacuum, there’s a force of almost 15 pounds on every square inch of your vacuum chambers. A 1 foot circular area has over 1600 pounds pushing on it. Vacuum systems with dimensions that hold things as big as filament spools are generally made out thick welded stainless steel. Heating in high vacuum systems is common to get to really low pressures and is done with specialized heat tapes frequently with fiberglass insulation blankets secured around it. Added - that’s overkill on heating but it’s very routine.
but his results showed lack of effectiveness, maybe because he didn’t also heat. If he had heated his vacuum sample equally as much as in his control sample, it surely would have been at least as good, and most likely better (or else why would industry bother with it?). Unfortunately, he didn’t do that experiment, so we don’t know how much better (grams removed) or how much faster.
Anyway, they’re obviously called vacuum ovens for a reason. i.e. both vacuum and heating to be applied simultaneously. Somehow that fact eluded him, or else he couldn’t figure how to heat his filament when under vacuum. It wasn’t a completely useless experiment, though, as it did show that vacuum alone is not effective enough to be worth the bother.
On the other hand, I just now looked i up, and freeze dryers used for food pull much closer to a full vacuum (<0.001 millibar), so maybe that’s the treshhold that’s needed, or maybe it just speeds things up substantially. Hopefully @SKL111 can offer some insight if he ever does grace us with a reply.
Just got done with Taco’s and I was surprised to see replies.
Here is Vision Miners Kit.that will include and Oven as an Option(yes same guys who make that bed adhesive that works on some bed surfaces) Filament Drying Kit – Vision Miner
The reason temperature has such an outsized influence is the vapor pressure curve. Things are a little different when the water is kind of stabilized in some hygroscopic filament, but the trend will still be there. Higher vapor pressure means more likely to go vapor phase for those unfamiliar.
At least that provides an easy workaround to the otherwise more difficult challenge of how I might get uniform temperature on the spool if the vacuum were applied first. And since it’s in a vacuum, it would presumably retain its heat for longer, so the faster I could draw the vacuum the better. On the other hand, it doubtless cools even faster to the degree that moisture is getting pulled out of it (right? evaporative cooling).
It leaves me undecided whether I need the better vacuum. I guess when in doubt, just go for maximum vacuum possible and don’t look back? Maybe that’s how they resolved the uncertainty of it.
Stupid side-story: I once owned pretty much the same vacuum gear as CNC Kitchen used. It looked identical and probably was identical. I used it to see if I could accelerate the degassing of mead that I was homebrewing at the time. At least for that purpose, It turned out to be surprisingly ineffective at the CO2 degassing maybe in part because I was limited to a vacuum that wouldn’t boil off the ethanol or the water. After years of the equipment just getting in the way and sitting around with no purpose, the oil suddenly started to leak out of the vacuum pump onto my floor, so I hastily got rid of the equipment last fall because it seemed unlikely I’d ever have another need for it.
It would also depend on the vacuum oven/oven based on the differing methods VM & SS show.
Here is the Top of the SS FDM Drying FAQ showing filament with moisture in it.
Dalton’s Law of Partial Pressures applies here. Dry air is as much of a vacuum for water as a vacuum is. The vacuum is just a brute force way of removing water along with nitrogen, oxygen, CO2, etc. Not saying vacuum won’t work. It absolutely will.
Thanks for pointing that out! Well, if that’s the case, I much prefer the dry-air make-up method. I wouldn’t be surprised if it were superior to the Vision Miner method, because you can monitor until it asymptotes, whereas you lose that level of control with the vision miner method. The Vision Miner method may be once and done, but for the same reason, who knows how thorough it is?
Pulling a hard vacuum is going to require a two-stage oil vacuum pump, and if my earlier experience with a cheap one-stage vacuum pump is typical, that can be a rather stinky proposition.
I don’t think you need to pull a hard vacuum, though. Just approaching a vacuum will still help dry it and probably be such a small difference you may not even notice.
And pulling a vacuum (even partial) will help to sweep moist air out of the filament loops on the spool. That will probably be a significant advantage on initial water loss.
What I see is a big humidity spike as the water starts leaving the spool in enough quantity. You’ll pump that away where I have to purge it. The filament and water doesn’t really behave differently. It’s just mechanically you’ll do a better job of getting the water out from between loops on the spool I think. How much difference that actually will be is hard to say but I’d bet you see it.
It might be hard to get the heat into the filament under a vacuum as there is no air to transport the heat anymore. We use a vacuum in the cryogenic industries to act as part of the insulation on liquid oxygen and nitrogen pipework which is in the -185 deg C range. It might be better to heat the filament first to liberate the moisture and then apply the vacuum to remove the moisture from the air, you would then need to introduce dry air into the enclosure and repeat the process until the desired level of filament moisture is reached.
But if Dalton’s Law is true, is there any advantage to pulling the vacuum? I suppose in theory maybe it’s faster, because it avoids the dilution problem.
Edit: The one advantage favoring the vacuum that I can think of is that you could utilize lower heat, and so maybe it’s more protective on the filament. Not really sure how important that is, but if so, then it’s an advantage.
Not really. At least not in terms of shaking water molecules to urge them to let go. There’s a fun calculator at Particles Velocity Calculator.
Put in a molecular weight of 18 (water), a temperature of 300K (27C, 80F) and the average velocity of a water molecule is almost 600m/s or 1800 ft/s give or take. Not much mass but the same as other water molecules.
Another interesting number is mean free path. Just change particles-velocity to mean-free-path in that URL and you’ll see how far a water molecule travels before it hits something else and it’s 131nm at 300K. I forget what pressure you said your pump can hit, but change to 0.1 torr and mean free path balloons to just about 1mm.
Added - that’s the advantage of vacuum. Even though the mean free path is still small, it’s way bigger than at atmospheric pressure so water that gets let go by the filament will be able to leave faster at pressure. That’s an advantage. Don’t know how much of one but it could be big. Only way to know how well it works is to test it.
In that world, giving a spool a shake really means nothing with regard to water leaving it, but can make a difference to pockets of trapped air, etc assuming at room pressure and not pumped down. Pumped down you’re wasting your time.
In terms of Vision Miner’s secondary advice, of using dry nitrogen or argon, I’m almost doing that, but presently with just normal desiccated air to keep the filament dry inside the drybox by supplying just a slight positive pressure:
I’m using an an oxygen flowmeter to dial the pressure all the way down to just above zero. I’ve been running it 247 for two days straight, and only just a little orange desiccant turned green, so extrapolating from that, I figure I can get about 10-14 days out of it before the ambient air burns through.
As you can see, I have extra desiccant in the drybox as a kind of backup and maybe a little extra scrubbing. After burning through an entire column on a previous trial though, it remained orange with no green.
If I need to do a purge on the drybox, as when first setting it up, I can turn up the flow all the way to 4-5lpm. I like having that kind of flexibility.
The purpose of this particular setup is to keep TPU dry while printing. That’s why there’s no bowden tube on the path coming out of the drybox. This is a harder scenario than when you have a completely closed path from drybox to printhead, which is the more normal case with other filaments.
I’m also using a wireless TH sensor inside the drybox to monitor the dryness of the air inside.
This is just something I lashed together. For a more polished setup, look into what MZip has published on makerworld:
By the way, as with MZips design, mine is powered by an aquarium air pump, so there are no significant pressures involved. Many thanks to @MZip in proving that such a pump is sufficient. IIRC, it may max out at around 4-8psi. I had earlier built one utilizing an air brush compressor, but that turned out to be the wrong approach for a whole host of reasons I won’t go into here.
As you can see, the total cost is quite low, and the benefit is guaranteed dry filament for the duration of your print. If you’re printing an expensive engineering filament, the cost is practically a rounding error in the grand scheme of things.
In a future version, I may take it a step further by inserting a stage or two of even better drying desiccants to further mop up after the first pass by the silica gel. That would take the air even closer to the Nitrogen or Argon dryness that Vision Miner is recommending in the screenshot above. That’s partly why I built this using quick-connects: it will make adding additional stages as simple as snapping them in place when that time comes.
Anyway, the point isn’t the detail of my particular build. The idea is easy enough, and there are probably many clever ways to do this. I still think @MZip’s design is the best place to start for anyone considering this.
Looks really good, @NeverDie. Also, I think it was @IslandBill who first mentioned an aquarium pump. It was brilliant. I think the barrier to entry would be lower with just a pump and container of desiccant, though. There’s only been 13 downloads and nobody has reported any results. People can do a quick and dirty check without much effort or cost though and that might get some independent reviews of the technique. The argon or nitrogen purge is indeed for all practical purposes the same as purging with dry air. Oxygen is the biggest difference but doesn’t really matter for this purpose. Both have very low to near zero water content which turns out is really important for proper drying. I think the Arid Air thing could be for when people want something more integrated or neatened up?
maybe in part because I was limited to a vacuum that wouldn’t boil off the ethanol or the water. After years of the equipment just getting in the way and sitting around with no purpose, the oil suddenly started to leak out of the vacuum pump onto my floor, so I hastily got rid of the equipment last fall because it seemed unlikely I’d ever have another need for it. 
