3D Printing Desiccating Filament under Vacuum

Discussion in '3-D Printing and Related topics' started by jlabrasca, Feb 15, 2020 at 3:54 AM.

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  1. Feb 15, 2020 at 3:54 AM #1

    jlabrasca

    jlabrasca

    jlabrasca

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    I have a couple of spools of wet filament that will no longer print cleanly. Lots of popping and strings and blobs.

    Looking at the available drying options, and and after getting a whiff of what came out of the lab oven when I tried to bake a spool of PLA, I decided to try putting them under vacuum for a few days.

    I tried to fabricate a vacuum chamber from an old wort kettle, but I couldn't get it to pump down to less than -0.2 bar. After a few fruitless hours trying to track down the leak I decided that my time was worth more than the price of an eBay degassing chamber. I am pleasantly surprised at how well this thing holds vacuum. I don't imagine the silicone collar seal will hold up to too many cycles, but for right now it is working.

    I threw in a couple of saturated-to-pink desiccant sachets so that I'd have something to look at for a clue if it is working, After 24 hours in the can, one or two of the sachets are looking distinctly mauve.

    I don't know how much water is coming out of the filament, but it is definitely outgassing something. When I cracked the chamber this morning the smell was alarmingly strong.

    Its pretty cold in the shop. and I can't think of an easy way to heat the filament while its under vacuum (The hotplate under the pot is really just for decoration).

    I am going to leave it under vacuum for the weekend, see if I get improved prints on Monday.

    20200214_142432.jpg
    20200214_142448.jpg
     
  2. Feb 15, 2020 at 11:05 AM #2

    dhbarr

    dhbarr

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    They sell flat heating pads for this exact purpose. Garden heaters would also work, or maybe a chicken heat lamp pointed at the side.
     
  3. Feb 15, 2020 at 11:14 AM #3

    David Schwantz

    David Schwantz

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    New to 3d printing.
    Why is it so important to keep it dry? What will happen?
     
  4. Feb 15, 2020 at 12:51 PM #4

    Charles_McG

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    Second sentence in the original post.

    Stringing
    Blobs
    Lumps
    Under extrusion
    Poor bed adhesion
    Poor layer adhesion
    Popping/snapping noise
     
  5. Feb 15, 2020 at 1:02 PM #5

    jlabrasca

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    Thought about a heating blanket wrapped around the can. What would be best, I think, would be a radiator inside the can and a chiller wrapped around the outside. Wonder how long you could run fish tank heater in a 70 torr ambient? >smile<

    What I really want to do is bleed hot dry N2 into the chamber and pump it continuously through a cold trap.

    The plastic is hygroscopic. There is more to it, and you will find some absolutely bonkers explanations when you google "wet filament", but some of the most obvious effects are due to the water absorbed by the filament "boiling" (coward quotes because of physics) in the extruder. It screws up the rate at which the material is extruded. The filament flows out too fast, or doesn't flow at all.
     
  6. Feb 15, 2020 at 2:29 PM #6

    cwbullet

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    Stringy prints, poor adhesion, under extrusion, jams. I an keep going but it depends on the filament and hydration level.
     
  7. Feb 17, 2020 at 8:38 PM #7

    jlabrasca

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    Check and check. First three layers are clean, then it started spitting and leaving strings. The last layer wasn't sticking to anything.

    20200217_120524.jpg

    This was the spool from the middle of the stack of three that I had under vacuum for about 72 hours. The hot plate was on "warm" -- which my $18 Etekcity pyrometer called 58°C.

    I was surprised that all of the spools in the stack were warm to the touch when I cracked the chamber. I wouldn't have expected a 60-70 ~100 torr ambient to do much to transmit the heat from the bottom of the chamber (even if the thermal conductivity of the plastic is higher than I'd have expected the bottom spool was held up by a couple of big glass marbles, so it wasn't in contact the bottom of the chamber).

    The only desiccant sachets that turned fully blue were at the bottom of the chamber -- directly in contact with the heated floor of the pot. I will clean off the bed and run a test print from the bottom spool -- but I am disappointed that the first test failed so early. If even the outer wraps of the spool are still wet, then the turns adjacent to the windows in the spools are going to be wet all the way down.

    I am going to try again, with just one spool in the chamber.

    edit: If the pressure gauge was accurate I was at about -0.9 bar when I cracked the chamber. The pump was rated for -0.82 bar when it was new (in 2001). I am guessing the pressure in torr wasn't as low as the double digits.
     
    Last edited: Feb 17, 2020 at 9:58 PM
  8. Feb 17, 2020 at 9:21 PM #8

    jlabrasca

    jlabrasca

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    Well that didn't take long. This is the spool that was at the bottom of the stack -- closest to the hotplate.

    Rather than go for the hat trick, I am going to clean up the printer and run a print with a dry spool, just to be sure that I am testing what I think I am testing (noticed some black gunk in that blue bird's nest -- the hot end is overdue for a scraping).

    20200217_130739.jpg
     

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