Drying filament under vacuum

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zemlin
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Joined: Sat Oct 21, 2017 2:02 pm

Drying filament under vacuum

Postby zemlin » Fri Jul 06, 2018 2:06 pm

I really dislike having to dry filament in the kitchen oven for hours and hours. At the day job I work some with vacuum chambers. I poked around the www a bit but didn’t find much information about folks using vacuum chambers to dry filament.

I’m going to give it a shot.

I ordered a 3 gallon vacuum chamber (a pot with a thick acrylic top) from Amazon, and an Inficon QS5 vacuum pump. There are cheaper pumps, but I don’t like to buy junk and reviews indicate they can't reach their rated vacuum level. The Inficon seems to have a decent reputation. I also got a tube of Dow 111 silicone grease to use on the seal on the chamber.

This pump is rated at a vacuum level of 15 microns, and it’s been reported that some will get down below 10 microns. Boiling point of water is about -60C at this pressure so I’m hoping that I can achieve a better level of dryness in less time. It should also work well for drying out my desiccant packets.

It’s a modest investment – about $350US total, and if I decide I need to add heat it could cost me another $100 – but I’m thinking additional heat shouldn’t be necessary at that level of vacuum. The pump shows up today. I already have the tank.

Might also be fun to play with drying fruit without heat.

If anyone out there has messed with vacuum drying at pressure levels like this I’d love to hear about your experiences.

Vice Chief
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Re: Drying filament under vacuum

Postby Vice Chief » Fri Jul 06, 2018 2:10 pm

I've been interested in similar ideas (but ended up with a lab oven instead - randomly found a great deal on one). Very interested in what you learn as I also need a vac setup for casting.

Phife
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Joined: Thu May 12, 2016 3:47 pm

Re: Drying filament under vacuum

Postby Phife » Fri Jul 06, 2018 2:57 pm

I use a vacuum pump and a chamber on a heat plate set to 50c to dry my Nylon, 15micron is more than enough, I only get down to maybe 50,000micron. Works well. I also line the bottom of the chamber with Silica beads so the moisture has somewhere to go. Although I'm not sure how necessary that is.

billbucket
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Re: Drying filament under vacuum

Postby billbucket » Fri Jul 06, 2018 3:20 pm

Interesting idea. I already have a vacuum chamber, but hadn't considered this application. Let us know how it works out.

zemlin
Posts: 358
Joined: Sat Oct 21, 2017 2:02 pm

Re: Drying filament under vacuum

Postby zemlin » Fri Jul 06, 2018 4:20 pm

Phife wrote:I use a vacuum pump and a chamber on a heat plate set to 50c to dry my Nylon, 15micron is more than enough, I only get down to maybe 50,000micron. Works well. I also line the bottom of the chamber with Silica beads so the moisture has somewhere to go. Although I'm not sure how necessary that is.

I'm going to keep the pump running throughout the drying process so that will extract any water vapor - but if you pull your vacuum and then disconnect the desiccant might be helpful.

MaxwellRi
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Re: Drying filament under vacuum

Postby MaxwellRi » Fri Jul 13, 2018 2:29 pm

That's a brilliant idea tbh. How long does this process take btw?

zemlin
Posts: 358
Joined: Sat Oct 21, 2017 2:02 pm

Re: Drying filament under vacuum

Postby zemlin » Mon Jul 16, 2018 4:30 pm

I've been working with this a little and it seems it's going to work well, but it's going to take longer to dry the filament than expected. The good news is it seems to get things far drier than cooking them in the oven.

My last test was to put my spool of NinjaFlex in the tank along with about a dozen Silica Gel packets. I tried drawing the vacuum down and then shutting the pump down after an hour - let it sit overnight but the packets with indicator were still pink. So I tried it again, but this time left the pump running overnight. The desiccant and the humidity indicator cards were all blue. I put the filament, a desiccant packet, and a humidity card in a ziplok bag - and put the rest of the packets and humidity cards in another bag for storage.
It's been over a week and the 10% indicator is fully blue on the card in the bag with desiccant packets. I've never seen the 10% dot go blue. Same thing with the filament spool. The humidity card in that bag starts at 30%, but it is dark blue - looking better than I've seen after cooking.

What I've learned is that the water that comes out of the stuff in the chamber ends up in the pump oil - so I'll need to monitor that. A tip I read online was to drain the oil and then freeze it - you can then pour off the oil and the ice stays at the bottom of the bowl - seems like a good way to recycle the oil and keep it clean. I bought a gallon of oil for about $20, and the pump capacity is about 12.5 oz - so it's not a big expense, but I wouldn't want to drain and pitch the oil after every big drying run.

I've been traveling on business a fair bit so I haven't had much play time - but I'll post more when I learn more.

zemlin
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Re: Drying filament under vacuum

Postby zemlin » Thu Jul 19, 2018 12:19 pm

Last night I loaded up the vacuum chamber with 4 spools of PC and Nylon filaments, and tossed a big pile of desiccant packets in as well. I started the pump and checked on it this morning after about 8 hours of operation. The oil level in the pump had risen to the very top of the sight glass, so I stopped the pump and replaced the oil. One of the desiccant packets is color changing pink/blue - it was still pink.

I drained the oil into a plastic milk jug. I was surprised by the amount of water that settled out of the oil after just a couple of minutes.
VacuumOil.jpeg


I started the pump back up and will check on it again this evening - it will have been running 24 hours.

When this run is over I'll try freezing the water out of the oil and pass the oil through filter paper so I can run it in the pump again. The oil is very light/thin. It is not cloudy when new, so I'm guessing there are some plasticizers or other compounds are landing in the oil as well - hopefully nothing that is too disagreeable to the pump.

Phife
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Re: Drying filament under vacuum

Postby Phife » Thu Jul 19, 2018 1:03 pm

This is why I pull a vacuum, shut off the valve and turn off the pump. I can hold my vacuum over night without the pump running. Dessicant is loose along the bottom of the chamber. You can get big jugs of dessicant on Amazon.

I dont have these "water" problems. Also, perhaps its dryer here than where you are.

zemlin
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Re: Drying filament under vacuum

Postby zemlin » Thu Jul 19, 2018 3:58 pm

Phife wrote:This is why I pull a vacuum, shut off the valve and turn off the pump. I can hold my vacuum over night without the pump running. Dessicant is loose along the bottom of the chamber. You can get big jugs of dessicant on Amazon.

I dont have these "water" problems. Also, perhaps its dryer here than where you are.

So how do you dry your desiccant?
If I am able to recycle the oil, I don't see the water as a problem. My thought is that leaving the pump running will result in a lower moisture content in the filament and the desiccant I'm drying.

MDVolle
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Location: Fullerton CA

Re: Drying filament under vacuum

Postby MDVolle » Thu Jul 19, 2018 7:28 pm

I'm really intrigued by this information -
My reading had suggested that the plastic materials needed to get warm to release the moisture and that a vacuum oven used the low pressure to speed up the process but there was no indication that it would actually remove the moisture by itself.
It also suggested that the desiccant WOULD release moisture with just a vacuum but the filament wouldn't -

I've been using an inexpensive large dehydrator (can fit 4-5 spools easily) and running an 8 hour cycle at 158F and it seems to work well enough but this sounds like it might do a better job of getting through the entire contents of the roll - low heat seems like it might not be getting through the entire spool when a fresh spool is tightly wound - I sometimes have to dry again about half way into the spool and don't know if that is new moisture or moisture I just didn't get out the first time.

Usually, Southern California is reasonably dry weather, but this season has been completely "wrong" - we've been having 65-75% humidity during the days (when "adapted" to a 30-40% range, this is outrageous - while I DO understand that its "Low" for some areas).
I have noticed more moisture issues and am realizing how much of a difference climate could make to your printing experience.

Phife
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Joined: Thu May 12, 2016 3:47 pm

Re: Drying filament under vacuum

Postby Phife » Fri Jul 20, 2018 3:56 pm

zemlin wrote:So how do you dry your desiccant?
If I am able to recycle the oil, I don't see the water as a problem. My thought is that leaving the pump running will result in a lower moisture content in the filament and the desiccant I'm drying.


Desiccant can be dried out in an oven, lots of instructions on the internet. But really, I don't use the vacuum pump often as I mainly print in PLA. I just toss out the spent desiccant. I got the color changing desiccant so I can tell when its used up.

zemlin
Posts: 358
Joined: Sat Oct 21, 2017 2:02 pm

Re: Drying filament under vacuum

Postby zemlin » Sun Jul 22, 2018 12:08 pm

That last batch of 4 spools and a bunch of silica gel ended up running for about 48 hours before the desiccant turned blue. I exchanged oil in the pump twice during the run and again when it was finished. I froze the water out of the oil and collected about 4oz of water (~120ml). I poured the oil through a coffee filter and it's back in the pump.

I assume most of that water came from the desiccant, as silica gel will hold up to 40% of it's weight in water. To get real numbers on how long it takes to try a spool of filament I might need to use weight. I have a digital scale that measures tenths of a gram - that and a nearly full spool might be adequate. Put the spool under vacuum and measure the weight every hour or so - should be able to get a feel for how long the drying process takes.

Printing some PC that was vacuum dried and the part looks mighty clean.

zemlin
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Joined: Sat Oct 21, 2017 2:02 pm

Re: Drying filament under vacuum

Postby zemlin » Mon Jul 23, 2018 2:38 am

I dug through the filament archives and found a neglected spool of Taulman 910. It had been stored in a bag with silica gel, but the humidity indicator in the bag showed at least 50% RH.
I weighed this spool on my cheapo scale with .1g resolution (but also a bit of hysteresis, so it's not perfect) and got 715.7g. I put it in the pot and started the vacuum pump. I checked the weight every hour or so throughout the day to see how the weight would change as moisture was extracted from the filament. The curve flattens out at about 10 hours. When I started this project I was hoping for a quicker dry than that, but I can live with this. For one, it's not occupying the oven and heating up the house for hours on end, and I also feel this is a more controlled drying process.
Capture.JPG

At this point I've drawn 2.1g of water out of the spool. I'm going to let this continue to run overnight just to see if this is the limit, or if more time will yield lower moisture content. I was expecting a more asymptotic curve than linear, but it looks like a pretty straight line.

UPDATE - I updated the graph after letting the spool sit under vacuum for another 20 hours or so (pump running) ... and it looks like it's continuing to dry out. I shut the test down at this point though as I have too much other stuff going on. I might run a longer test in the future - and maybe with different materials to see if that makes much difference.
Last edited by zemlin on Tue Jul 24, 2018 10:16 am, edited 3 times in total.

jon_bondy
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Re: Drying filament under vacuum

Postby jon_bondy » Mon Jul 23, 2018 11:27 pm

Do they make vacuum pumps that remove the water before it gets to the oil? I found these...

https://www.provac.com/blogs/news/16104 ... cuum-pumps
https://www.labconco.com/articles/how-t ... acuum-pump

zemlin
Posts: 358
Joined: Sat Oct 21, 2017 2:02 pm

Re: Drying filament under vacuum

Postby zemlin » Tue Jul 24, 2018 1:58 am

I work for a major manufacturer of high-end vacuum equipment. There are several types of dry pumps which use no oil, but they are far more expensive than what I'm using. What I've seen equipment to separate the water from from the vacuum line is also very expensive, so I don't plan to go there. Dealing with the oil really isn't a big deal.


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