Does anyone know the optimal storage humidity level for PPA-CF? See below for the gory details.
I’ve discovered that it is possible to over-dry PPA-CF. If it is too wet it blobs and the layer bonds are weak, but if it is too dry it becomes very brittle and breaks apart when trying to bridge. I’m working on a 3D printed guitar, where the soundboard consists of 2 solid layers, followed by 2.6mm of sparse infill, followed 3 layers of solid infill. The first top solid layer that prints on top of the sparse infill is the tricky part. If the filament is over-dried, it breaks apart before fully spanning 8mm gaps in the sparse infill below it. That, in turn, reduces the bonding integrity of the final two top layers, and the overall stiffness of the sandwich suffers and the internal damping increases. I’ve now printed two soundboards with dried filament that both look good, visually, but one sounds much better, indicating greater stiffness and lower internal damping. I suspect that the difference is due to slightly different moisture levels when printing. (Or it could simply be batch-to-batch variations in the filament material itself.) It is really difficult to measure the moisture level of the filament directly as the cardboard spool itself can absorb a ton of moisture throwing off weight measurements. Plus I don’t know what the ideal density should be in the first place. A easier solution is if I can keep the filament stored at an ideal humidity level and let it equalize to that level before printing. So my question is: what is the optimal storage humidity level?
So much going on here…
I don’t agree that it’s possible to over-dry PPA-CF. Bambu’s recommended drying settings are 100-140C for 8 to 12 hours - that equates to literally zero internal moisture.
I’d suggest checking out Bambu’s PPA-CF comprehensive guide.
How are you doing your drying? Is there a chance you’re actually over HEATING and causing some crystallization?
Also, are you annealing after printing?
Lastly…a single solid layer is probably a much better way to go versus a top/bottom skin with infill. Look at how carbon fiber acoustic guitars are made…they don’t use core.
Here is a spec sheet from Raise3D
They have the following note:
Note：
- Abrasion of the brass nozzle happens frequently when printing PPA CF. Using abrasion resistance nozzle,
as hardened steel and above grade nozzle is highly recommended.
- Please dry the filament at 80-100°C for 6-12 hours to restore the printing quality of Raise3D
Industrial PPA CF.
- After drying, we recommend to store PPA CF filament into Raise3D Filament Dry Box during the
printing.
- After the printing, it is recommended to anneal the printed part at 80-100°C for 8 hours.
- After annealing, max. 0.5% dimensional shrinkage could be observed in Z-axis depending on infill and
layer height, no obvious dimensional shrinkage in XY-axis.
- If PPA CF is used as the support material for itself, please remove the support structure after annealing.
Otherwise, the support structure could be permanently bonded to the model after moisture
absorption
This is from (edit-oops) bblcdn.edu on bambu ppa-cf
They note under “Recommended Printing Settings”
Printing and storage humidity:
< 20% RH (Sealed, with desiccant)
I’m drying in a toaster oven that I monitor with a thermocouple to verify that I’m at 110c (+/- ~5c). At first, I dried for the 12 hours recommended. When I printed with this filament, it tended to break apart as it bridged over the sparse infill. With a second roll that I dried at the same temp but for more like 6 hours, it printed more cleanly. So my theory was over drying. When I printed another guitar body with the same temp. drying and also for 6 hours, I got a much cleaner print. And then I did one more with the exact same drying and print settings - it looked the same but tonally sounded much better, so I thought maybe it was a different starting moisture. But now I’m wondering if it could have something to do with my H2D hotend fan. For the first successful print, the fan was starting to make some noise. I ended up replacing the fan before doing the latest print that is tonally superior. So maybe the better airflow of the hotend fan somehow affected the print?
As for annealing, the body has very large thin walls that I am afraid would totally warp out of shape with annealing.
PPA-CF is supposed to be printed without cooling!
This isn’t the part cooling fan, it is the hotend fan that prevents heat creep up into the cold-end.
I’m curious, Bambu states in their technical data sheet that cooling Fan should be On. Is that different than what you are talking about?
Edit I have no experience with the material so I am genuinelly trying to learn.