Question about storing and using filament  

RE: Question about storing and using filament

Posted by: @phil-15

After drying a spool of filament (at the correct temperature and for the correct time per the manufacturer's guide). Then I put that filament in a dry box with desiccant till I need it. How long will that filament stay dry and ready to print in the dry box? 
Does this dry box time vary by filament type?

Depends on the type of filament. For example, if your dry box is well sealed and your desiccant is not saturated, then PA6 is good for maybe 3-4 days before it has to be dried again. On the other hand, PET-G should be good for a long time. PLA can usually, depending on how humid your environment is, be stored outside a dry box. 

RE: Question about storing and using filament

For example, if you want to print with PPA-CF, PA6, or PA12, you must print directly from the drying unit; otherwise, print quality will deteriorate. If you’re printing with PETG from the drybox, a good amount of drying granules and a gyroscope will suffice.

RE: Question about storing and using filament

Thanks guys. What about filaments like ASA-CF and TPU95?

RE:

Posted by: @phil-15

Thanks guys. What about filaments like ASA-CF and TPU95?

ASA is hygroscopic but not that bad. If I'm going to do a long print with it, I'll pop it in the dryer first regardless. Better safe than sorry. 

TPU is a water sponge like nylon (but not as bad) and needs to be kept dry. I don't print a lot of TPU but after 3-4 weeks in a dry box I find I have to dry it again before a print. Basically if the hydrometer is above 15% and the desiccant is still charged, then it's time to pop it back in the dryer. Another thing about TPU is that never assume that a brand-new vacuum sealed spool is ready to print. It's an easy mistake to make. Here is an example of Siraya Tech TPU 64D that was in a factory sealed bag and immediately printed (on the left) followed by drying it for 6 hours

RE: Question about storing and using filament

I would also have a good hygrometer in the dry box to keep reading it.  hyiger's comment about TPU is correct.  TPU, even in a low RH environment will absorb moisture as it prints.  Need to print directly from a dry box with good desiccant.  My first attempts with TPU were from dryer to printer enclosure.  Start of print was nice.  By the time it reached 8mm, it was stringing and hissing. 

I am lucky, I live in a dry area.  Normal RH is around 20% at 22 degrees.  

A friend of mine that is new to 3D printing has a separate box with feed tube, for each spool of filament, hygrometer and activated alumina desiccant.  Even after a few weeks, the boxes are reading 10% RH at 25 degrees.  I also think the gauge they have doesn't go below 10%.  I know that mine read LO when they are blow 10% RH.

Any answer regarding dry filament and time depends on the humidity where the printer is.  If it is low, like mine, then the times are much longer.   If you are in the jungle, very much shorter.

RE: Question about storing and using filament

@phil-15, I'm going to give a different answer from those above (more similar to the experience @robin_13 mentions his friend having), and try to offer a constructive guess as to why the experiences differ. 

First: Dried filament I store in my dry boxes with a desiccant container (even highly hygroscopic filament) remains dry and ready for use for many months (that's being conservative, it can actually be years...more about that in a moment and a test I'm running as I type this). Not speculation, just what happens here. 

The difference may be in treating all "dry boxes" as equal. I suspect they are not. For example:

- A box with multiple assembled parts, using a large opening with a long separate flex seal in a groove, made out of a material that is more permeable to water vapor than others, and with multiple filament ports, and possibly a large surface area/volume (or any number of these characteristics)

vs.

- A solid container, made out of highly impermeable material (molded silicone-like material, for example) with a short seal that works due to the nature of the material itself (and the fit), not with a separate sealing piece, with a small internal volume, and with only one breach to the container (the minimum to feed filament). 

Put another way, if the dry box is truly well sealing and constructed out of material fundamentally impermeable to water vapor (in normal room conditions) (the second option above, let's call that a "good" dry box), and the filament and desiccant that goes into it is already equalized, let's say at 2% RH at room temperature, it is going to pretty much stay that way continuously (changing only in as much as the seal or properties of the box material are not perfect, which will always be the case to some degree, or if the temperature dropped a great deal). In this instance, the hygroscopic properties of the filament doesn't much matter; if the filament is in a 2% RH environment, it will equalize there regardless of its propensity to take up water vapor from the air (the rate at which it equalizes). Also, the desiccant sharing air with it in the container will be the first to take up water; that's the nature of desiccant (which is why we use it), so over time, you might see the desiccant gradually become somewhat loaded (time to swap it before it is saturated). 

I've had good luck with the particular approach I use of passively drying all new filament for a couple of weeks in a cabinet that maintains 2-3% relative humidity (without drawing much power, 2.5 kWh a month) and then moving filament into "good" (as defined above) passive single-spool dry boxes or vacuum bags (also "good" as defined above). I print directly from the dry boxes. I swap the desiccant whenever it becomes at all loaded. Periodically, I glance through the filament library for any rise in RH or darkening desiccant. I do not have to re-dry even highly hygroscopic filament before printing even after months...or years. 

The test I mentioned: As I started writing this, I looked in my filament library for a filament that is highly hygroscopic and which I have not used for a very long time. I selected a roll of Priline TPU that I haven't printed from for over two years. It has been in its dry box all this time and periodically had its desiccant container swapped for a fresh one (by design, easily done in seconds). Nothing else. I'm printing a simple part with it now. No prep, no re-drying. It is printing perfectly (with Prusa's generic Flex profile, as, apparently, I no longer have a profile for it...it's been that long). It just finished. Not one string, not one defect (I'll share pictures below). All to say that having an actual "dry" box, and periodically swapping desiccant, can maintain even more hygroscopic filament for years ready for use. This was not the most challenging test, but enough to back up the dry box hygrometers/cards indication that the humidity inside has remained below 10% RH all this time and the implication, therefore, that the filament would still be dry. I could find more challenging filaments to test, but I went for the oldest unused. My day-to-day experience over the past number of years is consistent with this test. 

(By the way, conditions here: 70-80% relative humidity in summer and 30-40% during the winter, temp 64-84 ºF.)

I have a bit of a "system" set up in my space (good for a personal maker space, likely less fitting for a farm) that is designed to remove the wet filament variable from my daily life. It's been working well. (It's great to no longer have to think about dry/wet filament in daily printing.) Instead of describing it fully here, I'll point to a recent YouTube video I put up that does a good job of laying it out (with links so you can go this route if interested). Take a look if you'd like more detail and chime in there with questions/comments.