Why is the quality of my nylon-cf prints getting progressively worse?
I'm printing a batch of similar parts one at a time on my core-one in Sunlu PA12-CF. In my first few prints the quality was essentially flawless. I've printed 7-8 of these parts now, and I've observed that the most recent few are noticeably lower quality. The surface finish is rougher, the edges are less well defined, the features that are meant to be straight have a slightly curve to them, etc. I've even seen that the supports are more messy and harder to remove.
I know nylon is a more complex filament than PLA etc, but I'm pre-drying it in a sunlu S4 drybox and printing it directly from there. I've had difficulties with pure nylon filaments in the past, but it seemed like the carbon fiber inclusion was making a big difference in ease of printing - at least in the beginning. Am I just fooling myself and the first few prints were lucky? Or is something maybe degrading or falling apart in the printer that is affecting the quality?
Here's a photo showing an early print with what I'd say is good quality:
Here's a more recent one that is definitely not good quality:
These are all being printed with almost the exact same settings in the same orientations with the same filament. Sure I've experimented with layer heights between 0.15 and 0.2, and tweaked the top z contact distance slightly, but nothing that should be causing such a big drop in quality - at least not that I'd have thought?
Thanks in advance for any help
RE: Why is the quality of my nylon-cf prints getting progressively worse?
I have not worked with Nylon myself yet -- but does the S4 drybox get warm enough to dry it effectively? I have seen recommendations of 90°C drying temperature for Nylon, but understand that the Sunlu S4 can only heat up to 70°C.
Also, what type of nozzle are you using? Is it still in good shape or might it be wearing out due to the abrasive fibers?
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I'm guessing that your S4 dryer isn't able to remove the moisture from the filament. The S4 doesn't reach the 80 degrees needed to dry your PA12 properly.
I would try the E2. Yes, it costs more.
Please keep in mind that the idler is not sealed. Everything that is moved in the Nextruder filament is exposed to humidity.
I have seen this phenomenon in my prints with PPA-CF. The Prusa XL is located in the basement at 45% humidity. The prints gradually got worse and worse, with more and more ozzing and so on.
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Nylons, especially PA6 and PPA not only need to be dry but need to be printed while drying and at least 80C. Also, storing in a dry box is not good enough (unless you live in the dessert). A dry box with < 10% RH is probably only good for 2 days before you need to dry the filament again. The purpose of a dry box for PA is to lessen the amount of time it needs to spend in the dryer. All this said, PA filaments are great but they are a royal PITA to work with.
As for the dryer on the Sunlu E2 or Creality Space Pi 4 gets sufficiently high enough to properly dry PA filaments.
RE: Why is the quality of my nylon-cf prints getting progressively worse?
I'm pre-drying it in a sunlu S4 drybox and printing it directly from there.
Could you clarify? Are you printing from the dry box with the heat running? As others have said, you need to dry at a high temp, 80-90 C and ideally keep it dry during printing as it will degrade in hours.
The Core One belts may loosen over time. Have you done the adjustment lately?
Have you done a cold pull and / or used the cleaning needle?
What nozzle are you using?
Regards,
Mark
RE: Why is the quality of my nylon-cf prints getting progressively worse?
Drying it at 70F for 24 hrs+ each time. If it was just a moisture problem I'd have expected to see similar results in each print but that hasn't been the case
I believe it's this hardened nozzle: https://www.prusa3d.com/product/prusa-nozzle-obxidian-0-6-mm-2/
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Yea, printing directly from the S4 while it is running. Pre-drying at it's maximum 70C for at least 24 hours, and then continuing at 70C while it runs. I understand a slightly higher temp would be ideal, but the info I found suggested that a lower temp could suffice if used for a longer period (i.e. a full day). The integrated humidity sensor as well as a separate hygrometer I bought on amazon and placed in the dryer show it gets down to less than 12% RH. Plus, I didn't see these issues at first which is what made me doubt it was purely a moisture issue.
I haven't done a belt adjustment, I can try that. Will also give cleaning the nozzle a go.
The nozzle is the 6mm ObXidian: https://www.prusa3d.com/product/prusa-nozzle-obxidian-0-6-mm-2/
RE: Why is the quality of my nylon-cf prints getting progressively worse?
The integrated humidity sensor as well as a separate hygrometer I bought on amazon and placed in the dryer show it gets down to less than 12% RH.
That's just the RH of the air inside the dryer. It does not tell you how much humidity you get out of the Nylon and how much remains inside.
Dry air in the box will help in absorbing water molecules once they come out of the polymer. But it's mainly sufficient heat which "knocks the molecules loose" from the polymer substrate, in my understanding.
RE: Why is the quality of my nylon-cf prints getting progressively worse?
I've been reading up on your earlier comment of a minimum meaningful temperature for drying and still am. What I found so far is that getting near the glass transition temperature of the material seems to make a dramatic difference in addition to the temperature dependency of diffusion. And the "Filamentum" doc stated that it is possible to permanently damage filament by over-drying. Interesting information, not done reading.
What I do know is that I've got a few spools that crumble to dust when you look at them sideways, not sure if they'll ever recover. Print nicely, though, if they find their way to the nozzle.
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Jürgen's point about not relying on RH inside the dryer is something I discovered. Some nylon's can absorb up to 10% of it's own weight in water. The filament is water logged, yet the hydrometer "says" 10%. The only way I know for sure is to weigh the spool once an hour and if the weight becomes asymptotic (doesn't change) then it's probably dry enough. This is why I've moved away from PA6 (which is a plastic water sponge) and print mostly PPA which is more forgiving.
RE: Why is the quality of my nylon-cf prints getting progressively worse?
I've been reading up on your earlier comment of a minimum meaningful temperature for drying and still am. What I found so far is that getting near the glass transition temperature of the material seems to make a dramatic difference in addition to the temperature dependency of diffusion. And the "Filamentum" doc stated that it is possible to permanently damage filament by over-drying. Interesting information, not done reading.
What I do know is that I've got a few spools that crumble to dust when you look at them sideways, not sure if they'll ever recover. Print nicely, though, if they find their way to the nozzle.
If the water molecules were just "trapped in a maze" inside the polymer structure, diffusion (Brownian motion, gradually increasing with temperature) would be the key ingredient to getting them out. And a humidity gradient (low humidity in the outside air) would ensure that more water molecules move out of the polymer matrix than back in.
But in addition, the water molecules "stick" to the polymer via adsorption. And in my understanding there is a very strong temperature dependence of the desorption process, i.e. the process of "knocking the water molecules loose". You need to give them enough thermal energy to come off the surface.
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PA materials are dried to a very low moisture content in professional injection molding. After removal from the mold, they tend to be relatively brittle and are therefore conditioned by intentionally adding water to the packaging in which the parts are stored. This restores the elasticity of the material.
RE: Why is the quality of my nylon-cf prints getting progressively worse?
Jürgen's point about not relying on RH inside the dryer is something I discovered. Some nylon's can absorb up to 10% of it's own weight in water. The filament is water logged, yet the hydrometer "says" 10%. The only way I know for sure is to weigh the spool once an hour and if the weight becomes asymptotic (doesn't change) then it's probably dry enough. This is why I've moved away from PA6 (which is a plastic water sponge) and print mostly PPA which is more forgiving.
That sounds very logical and is safer than leaving the humidity kit in a closed box.
Thank you for filling this gap in my knowledge.
Final question from me: What kind of scale do you use? How many decimal places does this type of measurement you described require?
Very interesting topic!
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Jürgen's point about not relying on RH inside the dryer is something I discovered. Some nylon's can absorb up to 10% of it's own weight in water. The filament is water logged, yet the hydrometer "says" 10%. The only way I know for sure is to weigh the spool once an hour and if the weight becomes asymptotic (doesn't change) then it's probably dry enough. This is why I've moved away from PA6 (which is a plastic water sponge) and print mostly PPA which is more forgiving.
That sounds very logical and is safer than leaving the humidity kit in a closed box.
Thank you for filling this gap in my knowledge.
Final question from me: What kind of scale do you use? How many decimal places does this type of measurement you described require?
Very interesting topic!
This is what I use: Digital Kitchen Scale it's supposed to be accurate to 1/10 gram so that's good enough for me. First you weigh the spool before putting it in the dryer to get a base line. I then dry it for 6 hrs, weigh it, then 1 hr later weigh it again. If it hasn't changed much (or at all) then (to me) it's good enough.
To the point of relative humidity display in a dry box, that it is just measuring the equilibrium between the amount of moisture in the box's atmosphere (assuming it's sealing) and the spool of filament. In other words, it's a measure how dry the air is in the box but not how dry the filament actually is. The air RH is a function of the desiccant (is it still doing it's job), how well sealed is the box and how slowly moisture is being pulled from the filament which is in turn a function of ambient temperature of the box. The desiccant pulls the filament and air to an equilibrium but in the case of Nylon that is hydroscopic this can take days or weeks even.
If you box says 10%, what does that mean? It means the air is very dry, moisture won't be entering into the filament. If the filament is already dry it will continue to stay dry. Especially though for Nylons is doesn't guarantee that the filament will be dry when you pull it out of the box.
If your box reads 25% it means the air is not dry enough for long-term storage, moisture will get pulled into the filament from the surrounding air. For PLA this is fine, PETG, PC, ASA probably OK. PA6/TPU definitely not OK. Doesn't mean though that your filament is wet. Just means you can't trust it to be dry.
One thing I've noticed. If your dry box reads 10%, you put filament in the box and you see the RH creeping up then the filament is still off-gassing moisture meaning it's not dry enough. One trick I played around with (before I started weighing) is after the dryer put the filament in a dry box without desiccant then watch the RH over 1-2 days. If it's between 10-15% then it's dry and if > 20% then the filament is probably still wet.
RE: Why is the quality of my nylon-cf prints getting progressively worse?
Very useful tips, thank you very much. I'll try it out and give you some feedback.
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I understand that moisture is the go-to diagnosis for nylon print issues, but I just want to emphasize that this was printing flawlessly a month ago using the same filament, dry-box setup, and settings. And it has progressively gotten noticeably worse. You can see it in the photos I included in the OP, and also in these:
If this was truly just a wet filament problem I would have expected to see it more consistently over the course of this production, but that hasn't been the case at all
RE: Why is the quality of my nylon-cf prints getting progressively worse?
I understand that moisture is the go-to diagnosis for nylon print issues, but I just want to emphasize that this was printing flawlessly a month ago using the same filament, dry-box setup, and settings. And it has progressively gotten noticeably worse. You can see it in the photos I included in the OP, and also in these:
If this was truly just a wet filament problem I would have expected to see it more consistently over the course of this production, but that hasn't been the case at all
I've printed enough nylon that when I see your photos, all I can think of is "wet filament". But certainly, this could possibly be mechanical as well. To rule it out, try printing the part with PETG etc as a comparison.