PETG Drying



  • What temperature is needed to dry PETG?

    Seen a few spool heaters but thing the 50C is too low?

    Typical defects from wet filament? Drooling, excess stringing, and occasional blobs on outer surface?



  • I'm not sure what the minimum temperature is, but I don't think 50c would be too low.

    I've used my convection oven set to the lowest temp (170F) for a few hours. I would check it every 30 minutes or so just to make sure it wasn't melting. The filament did soften a slump a bit, but didn't seem affected otherwise when printing, other than giving better surface quality. I would much prefer a food dehydrator with more controlled lower temperatures just to be on the safe side.

    If it's really wet filament you'll even hear hisses and pops and it's extruding. But it needn't be that bad to effect print quality. I've noticed rough surface texture and extra stringing.



  • @doctrucker Oh you'll know when it's wet. Surface finish is bloody awful and inter-layer adhesion is almost non existent. I once had a couple of reels of ESun PET-G that arrived nicely shrink wrapped but wet and I couldn't do anything with them. I gave them to some else who tried to dry them - I beleive he used 80 deg C or thereabouts but can't be sure. He managed to get some sort of prints out of them but they weren't great. I think they must have fallen overboard on the way from China or wherever, retrieved from the ocean, then shrink wrapped and packaged while still dripping.



  • I dry my petg when needed at 65C for 4-6 hours and that seems to work well.



  • 70C 6 hr here



  • I dry it around 60-65C for 2-4 hours, in a dehydrator. I monitor the humidity in the dry box as well, and dry it again if it hits 25-30%. That seems to be below the hissing & popping point, which is good.

    Be cautious about going too high in temperature - some spools can begin to deform, and you'll be plagued with feed problems from then on.



  • Isn't drying more a product of the difference in humidity and airflow than temperature alone.

    I.e. even a marginal temperature difference will dry the filament given enough airflow with low enough humidity, and even a substantial temperature difference can only absorb so much water without airflow.



  • @bearer That's my understanding. If you have a vacuum chamber you could dry it even faster since the boiling point of water drops in a vacuum.



  • When talking about humidity you need to be careful, relative humidity (expressed in %) tells you how saturated air is.
    So at 25°C air can have 20g of water per kg of air and that is 100% humidity. If you raise temperature to 65°C, air can take up to 204g, so that means relative humidity when you have 20g/kg is 32%
    So at "normal" conditions ant 25°C/50%rh you have 10g/kg and when you heat it up to 65°C you still have 10g/kg, so relative humidity is 6%
    But I think that temperature also plays in drying, it always helps if you get molecules moving faster.

    I once found these somewhere, and from what I tested they work. You basically set temperature as high as possible before glass transition.
    PLA - 4h@45°C
    ABS - 2h@60°C
    PETG - 2h@65°C
    NYLON - 12h@70°C
    PVA - 4h@45°C
    TPU/TPE - 4h@50°C
    ASA - 4h@60°C
    PP - 6h@55°C
    Dessicant - 6h@65°C

    Edit: Missing temperature



  • Thanks all.

    With metal powders if you picked the wrong temperature it sucked water out of the air rather than dry. I was worried that a too lower temperature may have the same issue with plastic.

    The food dehydrators look like a good option. Upto 70C ish and same price. Looks like I will need to cut out some trays but at £20-30ish I'm not overly concerned about cutting it up!

    I had thought that I maybe wasting time trying to sort part cooling ducts when my real issue was wet polymer. That said all of the worst edges are on one side of the part, so still safely in the domain of part cooling issues.

    I will order a dehydrator soon though.



  • @doctrucker said in PETG Drying:

    Looks like I will need to cut out some trays

    or print an extension. I just mocked up some 30 degrees sections and snapped together and on a tray with enough height to hold my widest spool



  • @DocTrucker

    Wes,

    Susi from "Rigid Ink" once sent me details of how to make a home brew filament dryer which she claimed worked really well. It's still on my "todo" list of things to make so I haven't got around to it but I'll see if I can dig out her email and forward it to you.



  • @deckingman I would be interested in that as well ...



  • @deckingman Me also please.



  • Some companies are now making real-time filament drying:



  • Ok, here is what Susi from Rigid Ink sent me

    But I haven't tried it so don't blame me .......

    You need of of these https://www.amazon.co.uk/Digital-Food-Dryer-Dehydrator-temperature/dp/B008MPBK8G

    and one of these https://www.amazon.co.uk/Whitefurze-Round-Cake-Plastic-White/dp/B00YJ83MHW

    These are the pictures she sent
    0_1560515096242_IMG_0131.JPG

    0_1560515106589_IMG_0133.JPG

    And this is what she said, quote:

    "As you can see, I just put the silica gel sachets on the grill of the bottom segment, then the reels in the top part.

    Hope this helps you out - I find it an essential addition for when printing with nylon-based materials and PVA.

    Just don't go over the Glass Temperature of the filaments being dried. The exception is nylon (Tg is ~41°C) as it has a very high heat deflection point (compared to the Tg) - I usually dry that around 55-60°C."

    End of quote............



  • This one looks like mine, but instead of buying the cake box, I just cut the middle of trays. It works.
    But I like the idea of drying the silica gel at the same time.



  • Thanks for the links. Will try at some point and report. Humidity sensor hooked up to Arduino may be investigated!


  • administrators

    @doctrucker said in PETG Drying:

    Thanks for the links. Will try at some point and report. Humidity sensor hooked up to Arduino may be investigated!

    you can interface a humidity sensor to the Duet as well:
    https://duet3d.dozuki.com/Wiki/Gcode#Section_M305_Set_temperature_sensor_parameters

    Channels 400, 401... are DHTxx temperature channels. The DATA line of the DHTxx must be connected to one of pins CS1, CS2... on the SPI bus. Specify the sensor type (11 for DHT11, 21 for DHT21 or 22 for DHT22) via the T-parameter. e.g. M305 P102 X401 T22 S"DHT temperature"

    Channels 450, 451... are as 400, 401... but specify the corresponding humidity sensor of the DHTxx

    So in theory you could have heaters/fans connected to a filament chamber that was controlled by the Duet and also fed the printer.



  • @t3p3tony sounds good, the mirror of a hopper pre-heat/dryer on a molding machine. Neat, and could keep the filament dust free too. I'll bare that in mind and ensure anything I buy for it can be ported across.


 

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