Filament Drying preliminary results

[MZip]

It’s not as unique as it seems, though. There are desiccant dehumidifiers with rechargers. And that drying fixture I built for this is just a test stand. There’s issues with it like to change the batteries in the hygrometers they have to be pulled back out after being siliconed in.

I had things that kept me from running the jade white rolls yet to get better/more data but I’m already very happy with just the silica gel performance. The kinetics are fast where breakthrough isn’t really an issue at least at low loading, and the exit humidity was low enough to peg the RH% indication to the minimum it can display - 10% - which is plenty low to dry filament effectively.

Since this seems to be a good setup, after the last tests comes turning it into a more friendly design, and slightly more compact form and increasing the flow by decreasing restrictions. The test stand design isn’t really practical for regular use but was necessary to sort out all the issues that turn a simple process complex and see what was and wasn’t important.

There’s more than one way to skin a cat but what I’m shooting for is simple, effective, low cost, easy to build, small, safe, low energy use, and not too much hassle to use. It will use desiccant faster than a recirculator but balancing that is the ease of regenerating silica gel. Plus, the pump helps to expel the hot moist air in the filament dryer while supplying dry air to replace it. All at room temperature.

A bit more to do but getting closer.

[NeverDie]

I think I now see a possible gotcha in the closed loop high heat recirculating air-desiccant approach. If you want a reliable design (and I assume we all do), then even with class h insulation on the blower motor or inline fan, there may still be risk of the motor windings getting too hot.

When it comes to motors, how hot is hot? | Plant Engineering

So, to mitigate, I may end up with something like a boiler draft-induced blower for moving the air, because those are many times designed to be highly heat resistant. Maybe all metal to rule out melting. So, notionally, something that looks like this:

https://www.aliexpress.us/item/3256806764469841.html?channel=twinner
This way the motor doesn’t have to be soaking in the elevated temperature while its working.

Unless somebody here has a better idea? It comes at a price. With @MZip 's earlier mixing design, a lesser blower could be used, because it would be operating at ambient. If you instead assume a much higher operating temperature, then finding a suitable fan/blower to circulate the air becomes a lot more challenging, for reasons explained in the above engineering article. The widely available ones that we’re all familiar with typically aren’t designed or rated for operating at higher temperatures. Maybe some of the limitations can be worked around, but it may require some thoughtful consideration and not just lashing commonly available gear togther. Since I’m building one, and not thousands, my bias is to spend a bit more if it helps to just get on with it and not stall. Buy once, cry once, and move on.

As an aside, this may explain why the Eibos rotisserie filament drier comes with a spare motor. They’re only expected to last around 1,500 hours, IRRC, probably because they’re operating at elevated temperature. So, that’s how Eibos dealt with this problem in their particular design.

As long as we’re on this topic, what are you all planning to use for ducting? High temperature silicone hose? Neoprene? Metal? This too can get expensive, so it’s yet another good reason to keep runs short.

[MZip]

The Sunlu S2+ also has a fan that is positioned just below the lower heater. When I replaced it with the Noctua, the temperature environment seemed pretty harsh. It’s hot enough that PLA softens down there when running the S2+ at 70C.

You should be able to use any number of shaft motors to have the motor body outside and put a fan blade assembly inside, though. You’ll get some heat conduction but you could use a motor with its own cooling fan to help deal with that like the one in your picture. It’s got a fan for the motor. Might be cheaper to roll your own. Plus you can mix and match motors and fans to get just what you need I think.

[NeverDie]

@MZip

You should be able to use any number of shaft motors to have the motor body outside and put a fan blade assembly inside, though.

Yes, exactly. Maybe there are other ways, but this keeps it simple. I’m no expert in such things, but a centrifugal blower (such as the one I pictured above) seems to lend itself to this kind of separation. Well, at least it can. There are also designs where the motor is embedded in it, but that would defeat the purpose. Unfortunately, most of the really inexpensive ones are like that.

[MZip]

Regular blade fans can work sort of ok too even if the blades end up being close to a wall or ceiling kind of like a ceiling fan. Even with almost no clearance you’ll still get stirring of the air around the blades. But yeah, if you are wanting to move/duct air through a bin of desiccant, though, you’d need something a little different.

[NeverDie]

It was language like this: “Max ambient temperature 60C” which had thrown me:

I had thought that a normal interpretation for “ambient” would have been temperature outside the ducting. Anybody else here read it that way? However, I think what they meant was the ambient air temperature around the motor, inside the duct. i.e. it shouldn’t pass air inside the duct that’s hotter than 60C, or you’d run the risk of the motor windings getting hotter than 130C. Why do I think that? Well, courtesy of this other company, which was less ambiguous:

where it says the fan should never be exposed to temperatures above 60C.

Frankly, it is NOT EASY finding a suitable fan/motor if dealing with temperatures above 60C. The few I’ve identified aren’t stocked on amazon and may need to be shipped from China, which is a bummer because of the shipping delay that comes with that.

[MZip]

There are bigger fans that do put the motor outside the duct and reach in with a belt to drive a fan on its own shaft but they are industrial sized. You might be able to diy with Erector Set style pieces, small toothed belts & pulleys, etc.

[NeverDie]

After marinating on the earlier engineering article whose link I posted above, it finally dawned on me that these dumb fans that I chose as examples are just on-off. However, if I were to run them (or similar) using a motor speed controller at a lower wattage–as I likely would–then that would buy me extra headroom that would be missing if used in their typical, dumb configuration. At least for me, that’s good enough to get me going on a first-pass FAAFO, as I’ll take care to keep it under observation during that phase.

[MZip]

Printing V2 now. It incorporates everything I’ve sorted out so far. To minimize pressure drops and keep flows up, most all of the external tubing has been converted to large diameter straight runs printed into the base. The silica gel reservoir is a tall and narrow-ish water bottle with large diameter straw mounted upside down - another way to minimize pressure drops and tubing.

Since the hygrometers get bedded into silicone and are a pain to remove, there’s a small amount of surgery/soldering to add wires that route to a battery bay in the back. The LR44 cells they run on are 1.5V so perfect for a single AA cell that will power both.

Anyway, progress again. I swapped to honeycomb infill on the dryer base so that it better stops the leaks gyroid just let run wild but it will still get a painting with thick cyanoacrylate glue of all the area that gets sealed up just to be sure it is all sealed up.

What I’m hoping for is better/higher flow that the user can decide how to throttle instead of just having to let it run full out. The silica gel reservoir is significantly bigger but no Drierite in this one. Just silica gel since it turns out that does fine. Kept the inlet and outlet hygrometers since that’s how well the silica gel is doing and if it needs regeneration. This will be able to use either indicating silica gel or plain.

Should be low/easy maintenance and provide a large enough flow of dry air for single roll filament dryer. This one is what I’ll test the jade white roll with to compare against the Sunlu S2+ with the lid propped open with a popular door prop here.

[MZip]

Just editing in place but interesting progress to report. I overengineered the aquarium pump bay with the walls a little tight. It turns out it really helped this project. The pump has a chrome plated outlet tube that turns out is also a flow restrictor. Found because I couldn’t get the pump to fit in the bay with it in place. We have enough restriction already so this is a huge bonus.

The tight walls on the pump bay made it impossible to place the pump in position as built so I opened up the pump and the chromed outlet tube is captured in the pump wall and has a small piece of flexible tubing to connect it to the actual pump module inside. Nix the outlet fitting and rubber tube and you can connect silicone tubing directly to the pump inside the housing and it now delivers a lot more air when the pump is turned up using the adjustment knob. It has significantly more flow available.

Inside diameter of that flow restrictor is 3.3mm on the inlet and 1.7mm on the outlet. They go from 8.55 mm2 to 2.27mm2 - it’s a big difference. This model adds its own flow resistance so if the pump needs resistance for some reason, there is some but this will definitely make more air available. Counterpoint is the silica gel will get used faster if people let it crank and depending on the state of the desiccant, exit RH% may climb. Fresh silica gel will do better at high flow rates than used silica gel already carrying water.

Going to spend more time with it and test more stuff / take the build as far as I can while a new adjusted base prints. The pump will get a few bits of foam tape to keep it from touching the housing and buzzing but it’s looking really good.

I know this concept works and calculations indicate that the silica gel reservoir will hold lots of water before the exit humidity will rise too much. It should remove the water equivalent to a 6 foot cube of 90% RH air down to an exit humidity of 10%. The cube gets a lot bigger at normal humidity levels. The kinetics are fast and the infrared images from the test stand looks like the water sticks as soon as it finds a good site to sit down on. So I think this is a slam dunk at this point after a little more tweaking around the pump.

It’s not perfect (a recirculating dryer stands to be more effective at actually drying filament) but isn’t bad. Silica gel is easy to regenerate so even working it hard it shouldn’t be too much bother to operate. Anyway, it’s coming along. I had hoped to not need a third print but I want to make certain everything works correctly before publishing it, but it should be soonish now.

[johnfcooley]

Just a thought, or question.

How would season change affect resullts?

[MZip]

As far as filament drying goes there should not be any difference from high vs low humidity days, cold or hot. With this providing dry air to the dryer, what would affect drying time and such would be the filament water content (edit - and how hard it holds onto water).

But in regards to the air dryer itself, what will happen on humid days is the desiccant will be used up faster/quicker. The way I’ll be running mine is to run it as needed until the exit hygrometer starts registering above 10% and then regenerate the desiccant.

But how much time before that happens will depend on ambient humidity, so hard to say. In my experiments with the test stand, it ran most of a day while it was raining off and on outside and doors and a window were open. The indicator never changed color, the exit humidity from the first desiccant bottle was always pegged at 10% indicated, and the heat in the IR images was only in the lower inch or so of the 1 liter bottle. This one is 2 liters so has even more reserve.

I don’t know how long it will last in regular use, yet. I’ve got all my existing rolls of filament that will get dried and moved to plastic cereal boxes with desiccant packs so it’s going to get a workout as soon as it’s built. That will also generate lots of performance data.

Longer answer than you wanted I think but hopefully complete.

[KanneKaffe]

Have you compared the energy consumption? Between drying the desiccant (after you have dried the filament with it) and drying the filament directly?

[MZip]

I haven’t looked at it in great detail but the big energy consumer is the filament dryer itself and those run for long times when people bake to a certain humidity value. Using dry air that humidity value in the filament dryer comes down like it does on a dry day. It makes every day a very dry day.

Shortening up that process can cut that energy in half or more if you cut the drying time in half or more. Regenerating the silica gel in a microwave uses lots of energy but the silica gel shouldn’t need to be regenerated very often and it’s just a few minutes. The silica gel gets used up in proportion to how high your ambient humidity is but preliminary tests look like there should be lots of capacity for drying a fair multiple of spools before needing regeneration.

Coincidentally, if your humidity is high and you use up desiccant fast while drying filament that means more time in the microwave regenerating and using more energy. But you would also be baking filament for longer times in a dryer without an air dryer if you can dry the filament at all. Savings will likely go up as your humidity goes up.

Good numbers aren’t available yet on how often the silica gel will need to be regenerated, though.

There are also other costs to wet filament - lost prints, wasted time, and wasted filament which all have energy costs too. It’s a hand waving answer but overall I think it will save energy but don’t have numbers to assert that.

[NeverDie]

I haven’t yet caught up on this thread, but as a brief tanget, I thought I’d memorialize that I found some fairly inexpensive (~$300) freezers on amazon which claim to reach -40F, and this appears to be confirmed by some of the reviews:

Amazon.com: SOUKOO Chest Freezer Super-low temperature Freezers 14℉ to -40℉...

There are even a number of <$200 freezers which claim they can reach as far as -46F, but I’m unsure as to whether that is mere “puffery” or whether they can deliver on it.

This is only noteworthy because I had previously thought that such freezers were easily >$2,000. This tact may be of interest to @IslandBill , who expressed interest in possibly working the temperature angle. To that end, I did watch a simple DIY video where a guy was getting 5% RH air for filament storage by pumping it into the cheapest possible walmart dorm room fridge/freezer:

Build the ultimate dry box! Use a mini-fridge for dehumidifying air.

Presumably, with a colder freezer such as the one I linked above, he could have done even better.

Anyhow, I have nothing more to say in regards to this, at least for now. Like MZip, I’m currently pursuing the desiccant angle.

[user_3026326371]

I see we are all getting into it now

As for the fan/motor I am able to shed some light on things…
There is two main motor types - long and short shaft.
The later is basically what find on any pedestal or bathroom fan.
The LONG shaft versions are designed to have the fan in the harsh environment while the motor is outside.
For example you fan forced oven uses them.

BUT we are not really getting over 70 degrees Celsius for most filaments we might us.
We have a lot of small and larger fans at work and one of my jobs if to keep them going rather than replacing them once a year or so.
These cheap cage motor fans are surprisingly resilient, especially the ones with just sleeve bearings.
Once the ball bearing ones are stuck you need a new bearing sooner or later while the sleeve ones are happy with a quick clean and a drop of oil.

As for the temps…
The solder joints are good for about 220 degrees if lead free.
The motor insulation on the wires goes even higher.
I use them in food dryers and literally any environment that won’t get hot enough to soften the plastic fan blades…
The max I had such a fan running in for several months was a box used to dry chemicals at a constant 105 degrees.
Only issues happening is those sleeve bearings running dry…

On the other hand we don’t really need much forced airflow in a closed box…
We only really need a half decent flow if using desiccant or such…
Even a passive heater in a short tube or such provides enough convection to get the box at even temps.

[user_3026326371]

Very cold freezers…

If you want to know how low a freezer COULD go you only need to check the refrigerant properties.
Even with just Propane you can reach minus 40 if you really wanted to but there is better refrigerants for those temps.

A few years back I needed something really cols in order to recycle some very costly chemicals.
Only had a tiny R600 compressor, salvaged from a fridge.
After trying all sorts of stupid things I listened to guy in our dementia ward at work (while he had a clear day).
He was a HVAC specialist back in the old days and suggested I should just use a long capillary tube that goes into a large diameter tube…
No TXV or such…
Turns out the man was (of course) right!
A far too long capillary tube created excessive pressure between compressor and evaporator tube.
The massive differential when entering the large tube caused an even larger temperature drop.
In order to ensure the compressor wouldn’t get a liquid refrigerant I added a reservoir - just a big, vertical tube with the in and outlet on the top so any liquid stuff can boil off.
Reached a solid minus 38 degrees under load and went down to about minus 45 without anything to actively cool.

Today though I would just use a larger compressor, more refrigerant and a higher flow rate.
Back then it all had to fit into a small housing…

[NeverDie]

@user_3026326371 It’s great that you know enough you could build one from scratch. More power to you. However, for a one-off that ideally would be some kind of jelly bean that “just works,” I’d rather not re-invent the wheel. Seems like in principle it should be possible to buy something turn-key with a compressor not much bigger than a coke can, in which case maybe the price would hopefully be proportionately low.

It’s easy enough to find units of that size, but not necessarily easy to find low-cost units of that size that cool to <-40C. Maybe something from aliexpress?

[MZip]

Final assembly is now done on my air dryer and it’s flowing air now to purge silicone seal fumes. I’ll be able to start testing Wednesday. Operates at room temperature with just a small aquarium pump to supply air and it should work better than the test stand since the first/only stage is longer and larger diameter than the test stand.

Found a few things along the way. The print itself is easy but there is a lot of assembly needed and some of it can make or break the project. End result is an attractive package that should help filament dryers big time with low operating costs and low maintenance as well. But if any mistakes it can be a round file result that takes some bought pieces with it. It’s almost how mine ended up but I managed to save it. Air leaks are the biggest issue and have a big impact on how well it functions. But care while assembling can cure a lot. Might need to revise some things to make it easier for non-technical skills people to build though.

But all it is is a pump blowing air through a bottle of desiccant. Test stand data indicates it really helps a regular dryer meet its potential for drying.

[user_3026326371]

I see the problem
Yes, Ali has everything you need and then some…
But even there is it hard to find a compressor kit rated for more than normal freezer temps.

What do you need those extreme temps for?
I just assume not really for filament drying…
For example, using Freon you can go to around minus 100 degrees Celsius with ease…
It usually isn’t used for anything above minus 40 LOL
Even R600 can be abused to lower than minus 40 if need be.

The problems with the design requirements.
Take a simple water cooler/dispenser.
A tiny compressor with a clever evaporator design keeps a reservoir cooled or for a a larger dispenser cools the outlet pipe directly.
The condenser in those cases can be like on an old fridge - just a pipe snake with wires to help the cooling.
To make it compact a fan is used and the air goes through a radiator like condenser - like in your pic often with a water line to keep the footprint even smaller.
So a cold trap is no issue at all, but cooling like a bar fridge sized box down to minus 40 and holding it is a whole different story…
Not just because of the requirement to have a reverse cycle or heating elements to defrost…
You can quickly end up with a can of worms and won’t be able to make heads or tails out it…