Most 3D printer filament soaks up water from the air, and when it does, the water passing through the extruder nozzle can expand, bubble, and pop, causing all kinds of mayhem and unwanted effects in the print. This is why reels come vacuum sealed. Some people 3D print so much that they consume a full roll before it can soak up water and start to display these effects. Others live in dry climates and don’t have to worry about humidity. But the rest of us require a solution. To date, that solution has been filament dryers, which are heated elements in a small reel-sized box, or for the adventurous an oven put at a very specific temperature until the reel melts and coats the inside of the oven. The downside to this method is that it’s a broad stroke that takes many hours to accomplish, and it’s inefficient because one may not use the whole roll before it gets soaked again.
In much the same way that instant water heaters exist to eliminate the need for a water heater, [3DPI67] has a solution to this problem, and it involves passing the filament through a small chamber with a heating element and fan circulating air. The length of the chamber is important, as is the printing speed, since the filament needs to have enough time in the improvised sauna to sweat out all its water weight. The temperature of the chamber can’t get above the glass transition temperature of the filament, either, which is another limiting factor for the dryer. [3DPI67] wrote up a small article on his improvised instant filament heater in addition to the video.
So far, only TPU has been tested with this method, but it looks promising. Some have suggested a larger chamber with loops of filament so that more can be exposed for longer. There’s lots of room for innovation, and it seems some math might be in order to determine the limits and optimizations of this method, but we’re excited to see the results.
Dumb question but… why not make a reel-to-reel drying system? It’s not as fancy but it seems like it would be faster than the dryer box method and more reliable/flexible than the “instant” drying method. Better yet, what about preventing it from absorbing humidity by putting desiccant packets in the filament storage box? I can’t help but feel that most instances that require drying filament can be avoided with some simple preventative measures.
Prevention is best, also for prolonged storage. As far as reel-to-reel drying, the method shown is still slow and inefficient, but better matched to the mm/s level filament consumption of the printer.
Granular drain cleaner (NaOH) is an excellent desiccant. Just put it in a jar with a perforated lid, and some loose fabric under the lid to keep the dust from coming out if you tip it. Keep your roll of filament in a plastic bag with the jar, and it will be bone dry.
And hey, if you handle it wrong, it can dessicate you too!
Yeah, nasty stuff.
It’s not very nasty if it’s either dry, or diluted in water. It’s at the point where it gets wet with water that nasty stuff happens – all the boiling and sputtering and melting flesh…
I’d go calcium chloride which is even cheaper and essentially harmless. (For storage. Here, he’s talking about a quick fix for already wet filament.)
Simply heating up the filament doesn’t drive off water very effectively. The hot air should also be dry, so calcium chloride of sodium hydroxide could act as an effective “getter” in the drying box and remove water from the air inside the box to speed up the process.
I very much doubt that with just a fan an some heating one can dry up in seconds a filament that slowly soaked air humidity: if it´s not that fast to soak in, it´s as hard to pull out.
Consider that 1 mm of filament on the reel is 19 mm of extrusion at 0.40.
If you’re printing at 80mm / sec, that’s 2.5 centimeters per minute off the reel. A dryer 37 centimeters long will give the filament 15 minutes in the blow dryer. Can you blow dry your hair in 15 minutes? Yep – even when it’s soaking wet, not just “humid”. The blow dryer isn’t even hitting all your hair for that 15 minutes; any particular section of hair is getting maybe five minutes of blow drying.
But it takes so long in an oven or dehydrator! Yep, the rate of evaporation is directly proportional to the wind speed. The air speed in an oven is roughly zero, so the evaporation rate is too.
Your hair is 40 times thinner than the filament. If you assume linear time vs. diameter, you would have to blow-dry your hair in mere seconds.
The water doesn’t diffuse into the hair as it does into hydrophilic plastics, it clings to its surface.
That said you can calculate how long the heat on the surface takes to penetrate through the material, just like sous vide cooking meat – there you need about 10 minutes for the first cm to reach 60°C. So 15 minutes to penetrate 0,9mm is should be enough, even if the heat transfer coefficient from air to plastic is worse than that of water to plastic.
Heat transfer into the material is far faster than water diffusing out of it.
“The air speed in an oven is roughly zero, so the evaporation rate is too.”
I think more to the point, the evaporation on the inside of a spool is going to be very slow. Hitting it with a hair dryer as it unspools should be a _lot_ faster.
(We have a convection oven.)
Now this is something clever that actually makes more sense in many cases, maybe you could even use it to be able to use grass trimmer nylon!
YouTube’s “Chickanic” in a video I watched recently, advises her audience to soak grass trimmer line in water to make it less brittle, so it lasts longer.
Yes, and the same with 3D prints using PA6 filaments. Dry the filament to print it (printing with wet filament is always a no-no) then soak the print in water to get a part that is more durable.
What’s old is new again: You’re annealing & plasticizing the nylon when you do this. It changes it from a highly crystalline solid to a more amorphous one capable of deforming a good deal before fracturing. Bonus: If you add water-soluble dye, you can color the molding with it as it is taken up into the structure as well.
FWIW we used to do this with model airplane propellers to color them and keep them from breaking and it worked so well we could literally grind them down on pavement without breakage.
Nice!
Thanks!
I’m loving his solution and video, so much better than all the ones with overly scripted, “advanced” methods/setup and more practical.
Glad he tried again with a reel from a dry box, more in line with how people store and use, versus allowing it to soak up as much possible yet was an interesting bench mark per se.
Possibly, improve the type of chamber so it handles/reflects the heat more efficiently. Maybe try a different direction/intensity for the air flow maybe?
I really liked this project. I’m impressed that he started with TPU. Moist TPU is the devil.
I’ve been printing with TPU for years and never seen any evidence of it absorbing moisture from the air.
I’ve read numerous time that TPU filaments are quite hygroscopic, and i will tend to believe they are. And since they are shipped without any protection (not in sealed plastic bag) i wanted to give a try and dry them.
But when I’ve contacted Ninjatek to ask, they answered me that TPU does NOT need to be dried, and that often “what customer think is a moisture issues is just the material being printed a bit too hot”.
And since TPUs glass transition temperatures are below 0°C, you can’t use this characteristic to choose a safe drying temperature, so it’s difficult to know at what temperature you could safely try to dry them!
One of the things I recently learned is that dessicant doesn’t really go any good with nylon filament because nylon is so hydrophilic that it won’t let go of its moisture no matter what the humidity of the surrounding air is. So it’s really difficult to keep nylon dry over long periods.
And even using a food dehydrator at full tilt boogie for 24 hours doesn’t quite get out enough moisture.
Having something like this that just managed to pull that last stubborn little bit of moisture out on the way to the printer would be great.
I toyed with the idea of Peltiers in some formation that would heat the filament, then cool it (using the same device) and somehow that would draw out the last of the moisture. But I never really got past the “thinking about it” stage.
>no matter what the humidity of the surrounding air
How about very close to zero?
Near as I can tell it doesn’t matter. The nylon won’t let the moisture go unless you heat it up. And I think one of my problems is that my food dryer doesn’t get hot enough to thoroughly remove moisture. I’m a little hesitant to monkey with it to make it go hotter on account of fire risk.
If nylon liked water more than any known dessicant, then surely that would make nylon the best known dessicant? (as far as dryness, not holding capacity).
I’d skip the tin can, and use a copper plumbing pipe.It can be long and can allow multiple heating spots and measuring points. Additionally its solder-able, and has screw fittings, and a T piece an the ends allows the filament to continue while allowing an easy in and out port for air. The decreased diameter will also increase the filament surface air speed. You can even introduce multiple in and out ports if the diameter restriction is too much. eg —— in — out — in — out — in — out — in— etc. All with simple hardware store parts.
Good idea. Putting the T in the middle, injecting hot air at the center, will allow an unrestricted filament path.
This is good!
20-30cm additional bowden tube with 100°c hot air flowing inside the tube?
I wonder if it would benefit from sending the filament spirally through the can, so it increases the time spent in the can, minus the need for more space?
This is coincidental. Only yesterday I was researching ways of drying PETG filament. I ended up buying a 4 spool filament dryer. From my own experiments, and advice from others, I am easily able to demonstrate the 3d printing differences between “wet” and “dry” filament. Air temperature and the amount of moisture that the air can carry are inversely proportional. There seems to be no “easy” way of measuring the amount of moisture that a particular filament has absorbed, but weighing a totally dry section of filament, and comparing that to the weight of the same diameter and length of “wet” filament, gives a reasonable indication of the amount of moisture that has been absorbed by the filament. This is something that I am still thinking about, but using accurate scales (I use gold scales regularly, so I’ll use those), recording the length of 10 grams of filament, then melting the filament over a stove and re-weighing the same filament, should give a fairly accurate measurement of the amount of moisture that was in the filament initially.