Remelting 3D prints in salt seems to be the
new hype! People have bombarded me with massages about
a video on remelting 3D prints in salt. So here we go. I printed a ton of different parts in PLA,
PLA+, PETG, and ABS remelted them in different grain sizes of salt, and tested them for their
strength. Don't tune away. This technique might be the most significant
post-processing technique for 3D printing there ever was! Let's find out more! Guten Tag everybody, I'm Stefan and welcome
to CNC Kitchen. Part of this video is sponsored by Audible. Start listening with a 30-day Audible trial. Get 1 audiobook and full access to the Plus
Catalog absolutely free. Visit audible dot com slash cnckitchen or
text cnckitchen to five hundred five hundred. Remelting 3D prints in salt seems to be the
new hype, and I see why. In comparison to my plaster annealing method,
you simply embed your 3D prints in salt, put everything in the oven to remelt the plastic
and end up with injection-molded strength 3D prints, or do you? After watching my video on plaster annealing,
a viewer named "free spirit 1" posted a video on his salt remelting method that he had been
working on in the past. Well, and it became kind of viral! In his video, he showed how the process basically
works, though I started further investigating it, looking at salt grain sizes, treatment
temperatures, dimensional accuracy, and, most importantly, strength. I'll also discuss to pros and cons of using
table salt and what alternatives there could be. Have you already tried this method on your
own? Then let us know how it worked down in the
comments? What applications do you see and is it worth
the effort? Since I wanted to know how and if the process
works with a broader range of materials, I printed samples in regular DasFilament PLA
and PETG as well as ESUN ABS and their highly requested PLA+. My primary test specimen was a square block
with threads on the top and a fitting nut. This gives me the possibility to check easily
measurable dimensions and take a look at the fine details of the thread and if they are
still working after the process. Of course, if you use this remelting process,
you need to print your parts with 100% infill, if not, you'll end up with big holes in your
part, and that doesn't only affect the look but will also makes the mechanical properties
very unpredictable. Let's first take a look at the main component
of this process, and this is the salt. Regular table salt is way too coarse and is
not suitable in many ways, as I'll show you. What you want is powder salt. Unfortunately this isn't something you can
buy in regular stores, at least not here in Germany. Powder salt, flour salt or popcorn salt is
available on Amazon, though at ridiculous prices, costing more than 10 bucks per kilo
and still might be too coarse to reproduce fine details. The thing is that your surface finish and
also dimensional accuracy is directly dependent on the grain size that you use. The finer, the better. I bought a large bucket of salt and used my
Thermomix, which is basically an expensive blender, to make my powder salt. Unfortunately, I quickly noticed that the
salt starts to smear and clump up during this process, so I was only able to process batches
of 300 to 400g at a time. If you also want to do this at home, pay attention
because I've already read a couple of times or reddit and facbook that people destroyed
their coffee grinder while trying to pulverize salt. Go in small batches and leave your machine
time to cool down. For my first tests, I let my blender run for
15s at full speed, though after the first remelting run noticed that this was still
too coarse and later let it run for 30s. That's what I used for most of my tests, though
in hindsight, I should probably even go longer to remove the last bigger grains and end up
with a really fine, flour-like consistency. After my first run, I also noticed that I
needed to have a vacuum close by because you generate a nasty salt dust, that potentially
starts rusting everything close by! Also wear gloves because the salt drys your
hands out and you don’t want to look like an Egyptian mummy. The next important thing is packing your parts
in salt because that will determine if the material can flow away in voids that you created
or if your prints nicely stay in shape, and you're able to reproduce all of the details. I used stainless steel GN containers that
are relatively high. For the 1.5l I used around 2.2kg of salt. I broke up bigger clumps using a sieve to
ensure that the salt is nice and fine. First I added a good layer on the bottom of
the container and then added the parts, while making sure that they are properly spaced,
to not melt together. Then I added more salt and tapped the container
regularly so that the fine powder was able to flow into all cracks and details. I topped everything up with plenty more salt
and then started compacting everything by just pressing everything together with a second
container. This is also why the powder salt is essential. Regular table salt or sand can't be compacted,
so that it holds it's shape. Powdersalt, with its fine and sharp crystals
though forms quite a solid mass if compacted and compressed. Compacting will not only make sure that no
voids are left, it will also ensure that the part can't deform anymore and therefore reduces
warping to a minimum. I only compressed the salt right at the end,
though looking at the fleshing that I got on some parts and some deformation, it might
have been better to compact several times while adding more and more salt, as shown
in "free spirit 1" s video. The height of the container is also important
in my opinion, because that will give additional rigidity above the parts and will not require
weighting the top surface during the heat treatment step. So if you only have a smaller pan, add something
flat and heavy to weigh the top surface down. Oh, and by the way. If you find this and my other investigations
helpful, make sure to subscribe and hit the notification bell. Let's next get to the heat treatment step. Suggested temperatures were 230°C for PLA
and even more for PETG and ABS for at least 45 minutes. That seemed a bit weird to me because that's
way above the melting points of these materials and even higher that you'd even print them. The thing is that long exposures to high heat
will damage the polymer by hydrolysis, oxidation, additive evaporation and some other reasons
more. So I thought that I start at lower temperatures
but add a BBQ thermometer to see what temperature we really have in the core of our salt block. Salt is not a great conductor of heat, so
it will take a considerable amount of time until you get to a kind of even temperature
distribution. If you go with higher temperatures, the core
will also heat up faster, but in the end, you'll have an overcooked outside and maybe
even still too low temperatures in the core. My lab oven doesn't have forced air convection
and in here, at a set temperature of 210°C, it took more than 4 hours to even get close
to that on the inside. My forced convection kitchen oven speeds this
process up a little but still takes a good 2h to get close to the target temperature. So if you want to take this method seriously,
get a BBQ thermometer and put it into the salt to time the point at which you can turn
the oven off. I usually did that when I was 10K below the
set oven temperature because that was a reasonable temperature gradient I was comfortable with. For my part, I let the prints cool down in
the salt overnight, roughly cleaned them from the powder remains, and then tossed them in
water to dissolve the rest of the grains on the surface. In the end I tried 180°C, 190°C, 210°C,
and at most, 230°C for the ABS part. 180°C up to 210°C was totally sufficient
for PLA and also PETG. All parts showed noticeable signs of remelting
with this very matte surface finish. The 3DBenchys that were only printed at 20%
infill also illustrated why fully dense parts are necessary for the process. The 100% infill Benchy came out nice though,
with great surface details. For ABS 180°C was just not enough. We're able to see that the part got soft,
but not all the way, so that it melted. 190°C looked already better. If we go way higher, in my case, to 230°C
the smell does not only get bad, but we can also spot severe discoloration and browning
of the parts that also shows up in the salt. The tensile test parts will later tell us
if this affected only the outer surface or, if we ruined the whole part. When comparing the different grain sizes that
I tried, we can also see that the finer the salt is, the better the surface gets. Though with my salt, I wasn't able to reach
the clarity of what "free spirit 1" showed in his video. Surface finish was very similar for all three
materials and this cooling nozzle also illustrates that you're even able to treat small and thin-walled
parts. I checked the amount of warping and deformation
first by simply screwing the nut on the thread. For PLA and PETG this only worked if I applied
a significant amount of force. The overall dimensions didn't change hugely
but still a litte and I rather think that the problem with screwing the parts together
comes from the porous surface which makes both inner and outer thread slightly bigger. ABS worked better in that regard and I still
was able to screw the parts together and overall dimensions didn't change a lot. My deformation analysis part also only showed
dimensional changes below 1%, which is a bit but still, way less than if you would anneal
without a medium that holds the part in shape. But let's now finally take a look at the most
exciting part. How did the strength of our 3D printed parts
change? Does this method fuse everything together
and heal the layer adhesion deficiency that we usually have? With plaster annealing, I also noticed that
probably the water in the plaster affected especially the PLA and made it very brittle,
so does this method, where no water is involved, affect the polymers less? For this investigation I printed a bunch of
my old layer adhesion samples, that have a bigger cross section as my mini sample. This way, surface porosity influences the
results less. These are for judging layer adhesion. Raw material performance as a reference value
was judged by simple dog-bone samples. Half of the samples got remelted in salt,
the other half was left as-printed as the untreated reference. All the tested samples were remelted at 200°C
set in the oven and I turned it off when it reached 190°C in the core of the salt block. The samples did look good with no major deformation
and only some showed a bit of fleshing that I had to trim away. Unfortunately, some showed bigger porosity
that might impact the results later. Regular, untreated PLA had a tensile strength
of the lying specimens of 61MPa; the untreated layer adhesion samples were only half as strong
with 31MPa. PLA+ has a slightly lower ultimate tensile
strength of 54MPa but yielded and didn't fail. The reference layer adhesion was 30MPa. The PETG samples were similarly strong, with
55MPa printed lying and an impressive 40MPa in the vertical orientation. ABS was the weakest with 40MPa of tensile
strength in its optimal position and only 14MPa of layer adhesion, which is often a
problem of this material, especially if it's not printed in a heated chamber. Let's now take a look at PLA, remelted in
salt. The samples broke quite violently and were
able to reach almost the strength of the ideally printed parts, which is more than impressive! If we take a look at the fracture surface,
the remelted sample is perfectly homogenic with only the porous seam around. The untreated sample clearly shows the print
lines. So the porosity that we've seen on the part
seems to be mostly only the first layer of salt that mixed with molten plastic and out
of which we've then dissolved the salt crystals using the water. This is good because that means with a smaller
grain size we should be able to reduce the porosity and also we didn't produce plastic
foam. Next, I tested PLA+. The material strength improved in a very similar
way and we almost reach ideal part strength. Unfortunately, I think some ductility is lost
because the material snaps without any significant necking, like we've seen it with the dog-bone
sample. Still very impressive results with a really
low scatter. Then it was time for PETG. I've tested more samples and temperatures
than I can fit in this video but here I’ll go into details on two where we can see something
interesting. If you by the way want to get your hands on
the complete results, they are accessible if you're a Patron or a YouTube member. During printing the samples I ran out of red
PETG so I switched to a roll of grey one, also from DasFilament, that was already open
for significantly longer. Both samples failed at around the same stress
level, though the gray one simply snapped whereas the red one yielded and necked quite
significantly. This might be due to the grey filament already
absorbing more moisture and becoming brittle, though this would require deeper investigation
for a definitive answer. The strength itself was remarkable, basically
reaching the one of the ideally printed part which clearly says that salt remelting PETG
fuses the layer perfectly together, creating a homogenous part with isotropic properties. Both PLA and PLA+ had a perfectly even fracture
surface, PETG though, shows a significant amount of fine pores, where it failed. I don't know if they result from moisture
or if they are the leftovers from the printing process that did not rise to the highest section
during remelting. What do you think? Finally, let's take a look at ABS. Here, I was able to increase the layer adhesion
by 150%, also reaching 90% of the strength of the dog-bone samples, impressive! The fracture surface doesn't look as even
as the ones of PLA but still no layer lines or porosity are visible. Just for completeness – the browned samples
treated at 230°C showed equal strength results, so probably only the most outer region is
affected at those higher temperatures. Those results again show the significance
of this method to get 3D prints just as strong as injection molded parts. Of course, it's a lot of post-processing effort,
but if you only need one or even 10, it's still way cheaper and efficient than investing
in an injection mold that costs more than your car! I think we're still at the beginning of researching
this method. I, for example, see the need to also take
a look at impact strength, different oven temperatures, other printing materials like
nylon or carbon fiber reinforced composites, how to design parts for this method, and how
to get them as dense as possible in the first place and so much more. Is salt really the best material for this
or can we use greensand, talcum or fine sand? But let me know what your verdict is, what
applications you see and if you want to try it on your own. Please leave your thoughts in the comments! Before we finish, let me quickly recommend
an audiobook that's especially interesting for makers and to which I recently listened
to, using today's video sponsor, Audible. Audible has an unmatched selection of audiobooks
and something for everyone regardless of whether you need entertainment while working at home
or if your aim is to educate yourself and learn something new. I recently listened to "Every Tool's a Hammer"
by Adam Savage, who should hopefully be familiar to all of you. The audiobook is read by himself, which is
great in the first place. He talks about his career as a Mythbuster
and, more importantly, his life as a maker. A great listen for everyone who is even only
the slightest interested in making, tinkering or in Adam Savage as a persona. Listen to this or any other audiobook for
free by starting a 30-day Audible trial. Get 1 audiobook and full access to the Plus
Catalog absolutely free. Visit audible dot com slash cnckitchen or
text cnckitchen to five hundred five hundred. No risk involved, and you can even keep all
of your audiobooks forever if you, at some point, decide to cancel the service. Thank you, Audible, for sponsoring part of
this video! Thanks for watching everyone, I hope you're
all doing well! If you found this video helpful than leave
a like, share it with the community and make sure that you're subscribed for more. If you want to support my work, head over
to Patreon, become a YouTube member or use the affiliate links in the description. Go check out my other videos if you currently
have more time than usual and want to educate yourself. Stay healthy, auf wiedersehen and I hope to
see you in the next one!
This method seems promising to reinforced parts. I wonder how well the surface finish would take to fiberglass welding also.