Filament Dryer

[jb_m4p]

Hey,

just a short question!
We only receive filament from Material4Print at our university. Soon there is the FormNext fair in Frankfurt where they are with a Filament Dryer system.

Do you use something privat for drying your filament? I always use their Filament and i never had to dry it O.o

Thanks for your replies!

[3dex ltd]

It depends on your environment whether you have to dry filament. In a dry room with little moisture in the air would be fine for storing filament. This is probably why you have never had to dry the filament.

Cheers,
www.3dexfilament.co.uk

[Todd-67]

I always store my filament in a zip lock bag with as much air squeezed out and a decadent pack. Never had an issue.

[curious aardvark]

yep my workshop is pretty much always arund 45-50% humidity and most of my regularly used filament is just stacked in the open.
Never had a problem.
Stuff like nylon is always left in bags with silicon sachets, but that's an extreme anyway.

[KDog]

I use a rechargeable dessicant in an waterproof file box.

[djprinter]

I use a rechargeable dessicant in an waterproof file box.

I do the same... I installed a waterproof storage box above my printer and and route the filament guide tubes into the bottom of the box. Within the box I have a paper lunch bag of drierite dessicant.

I have a humidity meter, and outside of the box it is usually 40-50% inside the box it's about 3%. Once it goes over 10% I recharge the dessicant.

[Ama-fessional Molder]

Depends whether you only require it to be dry enough to avoid cosmetic issues, or structural ones.

For the most part I think that the typical printer is not concerned with the extreme limits of performance, and so drying is less of an issue.

If you were pushing the limits of the materials I have come to the conclusion that a vacuum drying method is the most cost effective. You would use a vacuum pump and glass bowl setup like what people use for 2 part resin casting.

You first heat the filament to around 130-150F (55-65C), then while it is still warm put it under as much vacuum as you can for 20 minutes to a half hour. Voila, industrial quality drying at home.

Properly dried plastic also prints wonderfully compared to the same material when "wet". Once you dry it however, if you have a suitable means of storage you can likely leave it in there for months at a time without having to dry it again.

CA loves to disagree with me here (and his reasons are valid - most people don't have exacting structural requirements), however, I process plastic for a living so I love to rant about it. Since I enjoy it so much, here's my input on the subject if you do have structural concerns:


*Long version*

From my own experiments and experience with hydrolytically sensitive polymers (like nylon, PLA, and polycarbonate), it only takes around 15 minutes of exposure to 50% relative humidity to bring most materials to a moisture content which results in measurable degradation during processing.

It is possible to dry a material to a moisture content below that which shows cosmetic defects, but still degrades, and the reason is that the water is consumed during hydrolysis. Hydrolysis splits the polymer chains, making them shorter and weakening the material. It also causes a reduction in viscosity which I have not entirely determined the effects of on 3d printing, but in molding this causes flash.
Hydrolysis can also result in degradation of certain additives which, depending on the material, may be required to achieve excellent print quality. Some additives react with water, while others do not, and since manufactures typically don't inform the 3d printing community of what is in their filament it is hard to say.

For a semi-crystalline polymer minor degradation is not a major concern. Crystallization tends to negate it as long as you stay below the cosmetic limit of moisture content. If you are running amorphous filament, like polycarbonate, it's a real killer. PC doesn't have the crystalline structure needed to support it and relies entirely on it's very long chain length.


As an interesting side note (maybe I am the only one who thinks this is neat), the reason some plastics turn clear/translucent when molten and become opaque or diffuse when solid is because the crystalline structure interrupts the transmission of light. When melted, the crystals turn back into the disordered polymer chains and do not interfere with the light transmission nearly as badly. I wondered about that for a while before I finally made the connection and then had it verified.

[Alibert]

I also use vacuum drying and built my own vacuum-oven (heated-temperature regulated and with vacuum down to 1 mbar now with new dual-stage rotary pump). By reducing the vacuum to sufficiently low levels at a given temperature you go below the boiling point of water. With sufficient low vacuum you can make water boil at room temperature.

As with Ama-fessional Molder above, I use a lot of varied filaments including polycarbonate and since very recently PEI. The later two both absolutely need vacuum drying before attempting a good quality print, every time. I also found that PETG is very sensitive to humidity but seems to have a kind of threshold. In certain weather conditions it can stay out in the ambient for long times without problem, with others it is a nightmare unless vacuum dried. ABS also has that tendency but to a lesser extent than PETG. PLA I use rarely as it can not withstand high temperatures or is too brittle for pressure-parts in my setups.

As a chemist I would like to add some more on humidity. The equilibrium exchange of water molecules from the air to the plastic and back again depends partly on the plastic and temperature, but mostly on the concentration of water-gas molecules in the air. It thus depends on the absolute humidity as opposed to the relative humidity everyone keeps on mentioning. The definition of relative humidity is the actual absolute humidity divided by the maximum absolute humidity capacity the air can have at a particular temperature (hence relative). However the latter is strongly temperature dependent. A relative humidity of 50% at 18 Celsius means 7.7 grams of water per m3. A relative humidity of 50% at 32 Celsius means 16.9 grams of water per m3. Although the relative humidity is the same, the latter absolute humidity (on which the equilibrium with the plastic depends) is more than twice as high. You can google around for absolute humidity calculators and play around with them to get an idea. For example try to find out why there is also an industrial process called freeze-drying.

[Ama-fessional Molder]

Every time I mention that RH has nothing to do with it I get laughed out of the room. I only ever use it as a practical example that most people understand (as above). 50% RH at a pretty standard room temperature is enough for most people to understand how easily plastic picks up moisture. The problem though is that it is an incorrect metric to use and the 3D printing community is a bunch of home enthusiasts who have great intentions but are using the wrong information to make their claims.

I had one guy just screaming about it at one point, he was doing the math and everything to "prove" that simply heating the air up is enough to dry the plastic because the increase in temperature results in a drastic decrease in RH and as such the "air pulls the moisture out of the plastic", except molecular diffusion occurs as a result of concentration gradients, and hotter air still has the same concentration.

My own experience with a very expensive equipment and testing methods begs to differ. I asked him what the actual amount of water in the air was when warm vs cold and he claimed it didn't matter, then stopped replying.
Of course this can only be demonstrated with a moisture analyzer for most materials, although a home user could print out test bars and do a mechanical strength test to see for themselves if they have some means to control the environment of two samples of plastic.

Heat is beneficial however, as you need heat to excite the water molecules and coerce them to leave the plastic. You can very well lower the moisture content of a material with simply forced hot air as well, which is an old method used in plastics. The problem is you will never lower the it below what the gradient between air and plastic will support, whether it's heated air or not.

This is the very reason why industrial drying units have dew point measurement, not RH. Dew point is effectively (though not technically) a reading of the absolute moisture content of the air. Typically drying occurs at a subzero dew point and this is achieved by actively drying the air. Vacuum drying on the other hand doesn't rely on that at all, which is why it is so cost effective.



I am glad someone here agrees with me about drying their filament. I still want to figure out and design an automated vacuum dryer. The professional units are very expensive for something that could be done for a couple hundred dollars. All you need is a means to heat the chamber for X minutes and then draw a vacuum for Y minutes, then turn on a light when it's done.

[Alibert]

I totally agree with you on all points. Increasing the temperature only increases the maximum water content the air can hold (so may give you some more headroom if the ambient is near 100% RH), and improves the movement of the water molecules as the both the water and polymer molecules are more mobile. Increasing the temperature does not decrease the concentration of water molecules in the air, you can not make mass (water) disappear into nothing.

As to a personal vacuum oven, I use a large approx 4mm thick aluminium soup kettle (hotel kitchen size) with a 1" thick sheet of perspex on top. I have milled a 3mm deep round depression in the perspex sheet and poured a high temperature, high rigidity silicone rubber into it as sealing gasket. In the center of the perspex sheet I drilled and tapped entries for the manometer and ball-valves. I put a silicone heating ribbon around the kettle (stuck it in place with kapton tape) which I drive with a cheap chinese PID controller/thermistor. Around that a layer of 10cm thick glass wool. I have used a double diaphragm pump in the past, but now use a dual-stage rotary vane pump. The latter brings the pressure down to near total vacuum. I was surprised however at how hot the pumping end became, but seems to be the modus operandi of this type of pump. You will also need some good high temperature vacuum grease (laboratory supplies) to seal between the silicone and the rim of the aluminium kettle. Without it you will not get lower than 50-100 mbar in my setup due to residual leakage. I don't have a timer yet, but that should be easy to rig up.