investigation of salt annealing of transparent pla parts chapter II by Dr_Froggy_rD

Last crawled date: 3 years, 4 months ago

Hi everybody,
The second chapter about getting a quasi transparent part from a 3d printed /FDM object by remelting the part immersed in salt. Also described as annealing or sintering.
My first thought was how to sinter the pla in a very viscous liquid without reaction possible. Therefore I came to the idea of silicon oil or wax.
Making a negative mold of the form....
Not very convincing at all.
Even heat polishing with a heat gun the surface with silicon oil applied...resulted in an art of frying the pla... not great.
So I reconsidered this. I thought instead if I can coat the surface to avoid direct contact of the salt with pla and if I can use a sacrificial coating that can be easily removed.
Therefore, I tried a commercial pva glue for wood (pattex) but I believe other brands like from uhu will do the job as well. I tried pvp too but was not successfull (however I believe this should work too).
As one can see on one picture with three dices and annotations, some calibration dices were coated on three consecutives sides. Let to dry and recoated. Once dried, immersed in salt as on chapter one explained.
Then heated to 185°C for about 2 hours. Took out from the oven and cooled down fast.
Once cooled the dices are recovered by immersing in water. Using purum ethanol and brushing with a toothbrush allowed to remove the sacrificial coating left over.
However, the coating at those temperatures turns to caramel kind of.
One can see frost like faces (blue arrows) and mostly clear faces.
As I obtained encouraging results, I carried out the experiment on fully coated dices (I heat fused a left over pla filament on one edge forming a hook at its other end to be able to manipulate the dice and coat it completely. Drying by hanging over a string)
Then I performed the same procedure immersion in salt at 170°C only for to hours. Then cooling down , removing the salt and the coating (water and purum ethanol).
The dices obtained are pretty transparent!
The process still needs to be improved... nevertheless, it can be now further improved by any of you! This show one way to go!
I expevt anybody to perform a lense with this methodd!
In my case, not having 100%infill is a killing criterion, I observe a lot of bubbles!
Also the material flow and temperature of extrusion.! It must avoid entrapping any air!
Maybe another brand for the coating do not caramelize, or fries....
The salt fineness?
Using an inert coating is important but it must be easily removable.
Remelted Pla is prone to colouration.
NOTA: a dummy object is included to be able to publish this!