It was CNC Kitchen’s work on annealing that made me worry that it was too hard to do (rememeber all those PLA prints he tried to anneal, but largely deformed them instead?). However, he reports that CF Nylon doesn’t deform under annealing (High Speed Printing: Hot End, Temperatures, Silicone Sock and Materials — CNC Kitchen). Is it true? And, if so, why type of nylon?
His comment makes me a lot more optimistic about trying annealing.
I read somewhere nylon gets stronger(?) from humidity. So maybe anneal in a steam cooker lol
There is different types of nylon and they behave differently.
Additives affect this but also change some fundamental properties.
Annealing is a fancy terms for making sure whatever went wrong in the model fuses together properly.
Problem is, as you noticed that finding the right temperature and exposure time is near impossible.
When the surface seems perfect the inside is still too cold, when the inside is perfect and the temp not perfect the model already starts sagging…
I only used CF filament a few times and that only in sample size volumes like 10 or so metres of filament ordered.
But I did print with plain Nylon quite a bit in the past, usually for larger sized models.
The warping you fear is quite often a combination of factors, not all of which can be fully eliminated.
Take the plate adhesion - we need this to be strong because the tiny temp difference between plate on top of the layer is already enough to shrink the top.
From there we rely on an even temp inside the build chamber to prevent overhangs and such from going rogue…
Ideally we would keep the chamber temp just above the temp that makes the nylon too soft…
One completed the print does not cool evenly either, especially if all bed heating turns off while the chamber fan kicks in for cooling…
Means the nylon shrinks differently…
A lot of this can be compensated for, even if it means splitting a model.
What we can’t change is the general behaviour of these filaments.
Here is something you can try:
Print a thin 3mm strip.
Let it all cool then place back on the bed and check at what bed temp the strip starts to soften.
By soften I mean having the stiffness reduced, not actually going soft!
Note this temp somewhere…
Now keep increasing the bed temp, give the piece a bit of time to reach it, flip over and check if the hot side starts to soften, actually soften.
I use a cheap toothpick - if it leaves a dint it went soft…
This is your second temp to note down.
For the first CF test print something you would be prone to warping but still small enough to not cost too much.
Anneal for at least one our at just below the first temp you noted.
Preferably in a well controlled and fan forced chamber with enough silica gel.
Without opening to check ramp up the temp to about 10 degrees below the softening temp - your second temp you noted.
Anneal for 30 minutes then allow to SLOWLY cool down inside the closed chamber.
If this, naturally takes less than an hour lower the temp incremental.
2 to three hours to get back to room temp is good.
If it is possible to keep the fan running turn it off 
Check the model for deformed or shrunk areas.
In case nothing happened and the outcome is not good enough in terms of strength or surface finish try again but increase the second temp to just ABOVE the softening temp.
Be aware though that this can result in more deformations, so it can be beneficial to leave the supports on the model.
In case the model did deform you can try the sandbox method.
Mix some green sand but stay on the dryer side here, just enough to make the greensand formable to hold a shape.
Use a large enough wooden box to place your model in, after filling a few cm of sand and stumping is firm that is…
Build up the sand layers and tap it firm everywhere, especially against and around the model.
In case your model shall not risk getting and rough texture from the sand you can dust it with baby powder, corn starch and such.
Helps to not end up with stuck sand on the model in places hard to reach…
Place the box in your oven if it has a half decent temperature control.
Start at just under 100 degrees Celsius to drive the moisture out of the sand.
This will make the nylon absorb some of this moisture.
You might have to start with a filled sandbox but no model in order to work out how long it actually takes to fully dry the greensand.
Make sure to open the door for a second or so a few times per hour so let the moisture out if you oven does not have steam coming out somewhere when cook some juicy chickens…
Once dry you keep increasing the temp until you get above the softening temp.
Don’t go too far though as then the nylon will get sticky again and bond with whatever it is encasted in…
Keep this temp for 45 to 90 minutes depending on the size and infill amount of the model.
Then turn the oven off and let the box cool down - preferably over night as it will take quite some time.
Leave the oven door closed.
You will still encounter shrinkage for things like a square box and it’s flats but with the sand around the chance of things moving out of shape and place is drastically reduced.
I only use this though for parts I know will be subjected to rough handling and brute forces…
Here’s the quote that’s of interest (bolding is mine for emphasis):
By the way, if you remember my first video on the VORON you’ll know that I had huge problems with the Carbon Fiber Nylon that I used for my parts because they slowly deformed over time. People were asking if I already fixed that. Well, I could have just printed all parts from ABS and be done with it, but that’s not how I and also you will learn a lot. Instead, I’m currently working on a material creep test that I came up with. For that, I printed test pieces of a bunch of different materials that I load in compression by tightening a bolt with a torque wrench. Torque and the pretension in the bolt are proportional to each other. So, when the material creeps away under the load, the pretension will reduce, and I will be able to retighten the bolt again by some amount that I measure with these dials. This is what I’ll be doing in regular intervals at ambient and at slightly raised temperatures to compare how different materials behave. If you have any thoughts on that procedure, please let me know and also make sure to be subscribed and have selected the notification bell to not miss the results. Despite these tests that are ongoing, I actually got the Carbon Fiber Nylon to work as well. How, you might ask! Well, I annealed some of the parts at 160°C for two hours and had them now installed on my VORON for several hours of high temp printing without any sign of deformation so far, pretty impressive! The cool thing about annealing Carbon Fiber Nylon is, that it basically doesn’t deform during that procedure in contrast to PLA! I’m still not sure what I’ll be using for the re-build and will decide that after I finished the creep test.
I have procured a chinese blast oven, now sitting in my garage. Just $300, delivered. I have used my own temperature probes to confirm that it is working correctly. Current plan would be to print in the X1C and let ti cool to ambient inside the X1C. Then, remove the print (unsure whetther to leave it attached to the garolite build plate) and then dry it at 160C for maybe 2 hours (as that number if what worked for stephan at CNC Kitchen). It would likely auto-release upon cooldown unless I were to secure it witih vision miner bed adhesive.
Nice findings and explanation indeed!
So CF nylon really is best for those tough tasks after all, will keep this in mind for future projects.
What do you think if the main factor here?
The printed part drying up or the high temperature treatment releasing stressed while also increasing the strength ?
With the much lower moisture absorption of CF nylon blends I wonder how far we can go with such treatments.
What would be the maximum durability and strength we can reach…
Compared to just printing it and leaving the part like this.
A read a few study papers in regards to fillers and additives to change the properties of extruded of blow moulded plastics.
While fibre based fillers as still the preferred option there is a trend towards polymer based fillers that change the material properties during the heating/melting process and set upon cooling down.
Will be interesting to see if some of those patents will make it into our filaments one day.
Well, the HDT is well studied and well known, and it’s in any datasheet that’s worth a damn. The difference between annealing and not annealing is night and day. So much so that I’m tempted to say that not annealing a fiber filament makes printing with a fiber filament (glass or cf) nearly pointless if not absolutely pointless from a functional standpoint, although I guess some people can justify it simply because they like the aesthetics of it.
Are you suggesting that a non-annealed cf plastic is worse off than a non-annealed non-cf plastic?
No, of course not. I’m not suggesting that.
