Drying Times and Temps in Dehydrator  

RE: Drying Times and Temps in Dehydrator

You are right about experiment design being key and I've certainly learnt plenty (and no doubt more errors yet to make!).  For example, scratching my head on the Dry Cabinet data not being as slow as I expected, it turns out my first data point is actually 90min in length (not 15min as with the Vac and Dehydrator).   It would flatten the first part out for the Dry Cab curve.  I've also got the same issue with the ePA-CF data as I did them in pairs.

Here is a link to the spreadsheet https://jmone.org/jmonenextcloud/index.php/s/GKoJEmayEaBCRNG with times and measurements for each filament so far.  You will see that the PLA immersed in water did gain 1.2% but then when I left it it air it started to dry back out.  Also looking at the data, the sample that had gained the most went into the Vac Chamber not the other way around.

We have discussed using both Vac+Heat many times and it is a method I successfully used previously to dry my last spool of ePA-GF when the oven alone was not working (or working to slowly).  I know you don't think Vac works well from your experience, but this is also where differences in equipment and environment (like room temp) may play a part.  Mine will pull a hard enough vacuum to boil water a 25c.  I don't think you responded if your vac can do this?  If it is weaker then I'd assume it would take longer.  Then again, this is about working with what we have around the house anyway - not building a nuclear reactor.   

Anyway, back to improving the the experiment design.  I think the water and humidity box is just adding complexity.   I've also had timing issues with samples being processed at different times to each other.  I figure the simplest way would be

- 3 x samples of PLA, ePA-CF, PETG, and ePC

- Leave them in Atmo till they finish gaining weight, at which point I'd dry each set using:

- Dry Cab (the PLA, ePA-CF, PETG, and ePC can all go in together) - at room temp

- Vacuum (the PLA, ePA-CF, PETG, and ePC can all go in together) - but at what temp???

- Dehydrator (the PLA, ePA-CF, PETG, and ePC could all go in together) - but at what temp??? ..or..

- Dehydrator (PLA @ 50c,  PETG @ 65c, and ePC & ePA-CF @ 70) 

Thanks

Nathan

RE: Drying Times and Temps in Dehydrator

FWIW, Here is the chart so far with ePA-CF.

- Sample 2: Dehydrator was at 70c: Sample used had gained 5.14% since printed (left in a 100% RH box for a week then left in Atmo for 19 hours before drying) 

- Sample 1: Vacuum was strong enough to boil water and the vacuum chamber was on a heated plate keeping the samples inside around 35-40c:  Sample used had gained 5.11% since printed (soaked in water for 5 days then left in Atmo for 36 hours before drying)

- Sample 3: Dry Cabinet reads 0%RH: Sample used had gained 0.21% since printed (left in Atmo @ 50-60% RH for a week before drying)

My (unscientific) thoughts so far are:

- These are much wetter than the PLA and taking longer to dry for VAC and Dry Cabinet, though the Dehydrator at 70c is making short work of it.

- Just left in Air, ePA-CF gained 2.59% in a day.  This stuff needs to be stored well, and dried before printing

- All three methods work by creating a lower RH environment than the sample allowing migration of moisture to the Air, and

- The warmer the sample, the quicker the transfer seems to be.

Thanks

Nathan

RE: Drying Times and Temps in Dehydrator

@tim-m30 & others.  I've been thinking more on a design that you may agree on that fits with the gear I already have.  All my filament is stored in the 0%RH cabinet so they should be pretty dry.  My OHAUS scale only goes to 200g but it reads down to 0.001g.  So how about:

- Take a 3 x 100g (ish) filament sample off the spool and tightly wound it (so it fits on the 19cm bed of my OHAUS scale).  Use a soldering iron to weld the sample ends so it can not unwind

- Just incase, dry the samples according to the Print Dry recommendations of PLA @ 50c 3H,  PETG @ 65c 3H, and ePC @ 70c 6h & ePA-CF @ 70 12h

- Store all the samples in my 0% RH Cabinet as the others are being dried.

- Measurement all samples at the same time so we have a starting "Dry" weight

- Leave all samples in Atmo?? or a 100% Humidity Box?? till they all stop gaining weight.  

- Take measurements along the way so we have both an ending "Wet" weight and how long that takes

- Dry one of each sample in the Dry Cabinet (all at once)

- Dry one of each sample in the Vacuum Chamber (all at once) - but at what temp??

- Dry one of each sample in the Dehydrator, but all at once at the same temp???, or PLA @ 50c,  PETG @ 65c, and ePC & ePA-CF @ 70 ???

I'm away most of Jan for summer so the testing will need to work around that.

Thanks

Nathan

RE: Drying Times and Temps in Dehydrator

On the ePA-CF Front (still going):

- Dehydrator: Finished in 7:15h

- Vac: Still going, 21:30h so far and sample has dropped to 0.74%

- Dry Cab: Still going, 36h so far and sample has dropped to 0.77%

RE: Drying Times and Temps in Dehydrator

...and here are the raw graphs (web link so it should update when I update the chart).

Thanks

Nathan

RE: Drying Times and Temps in Dehydrator

Sorry for this long post.  But I tend to get pedantic when measurements are concerned.  I spent too many years designing systems that were making measurements traceable to standards, and working with people who really didn't understand the concept of measurement error and how to minimize errors: I was almost always in "trainer" mode with peers, clients and customers. Old habits and all...

Let's say you are testing four drying methods:

1. Free Air
2. Dryer at 50c
3. Vacuum at 23c
4. Vacuum at 50c

You then need four samples, each sample wetted with the identical method and specifics.

Wetting plastics can happen fast, but the mobility of the moisture intrusion is unknown (I don't have access to published test results that show results for testing this effect).  But, experimentation shows it takes time to fully saturate a solid plastic with moisture.  Plots available online support this conclusion; even immersion does not saturate plastic in a way we'd call fast: but is probably the quickest way to add moisture in the outer layers of the solid.   Moisture - it seems - migrates on a molecular level between the plastic molecules.  This speed is dependent on many factors; and can be accelerated with heat.  Thus, boiling water or high temperature steam is used to accelerate the process.  With our desire to understand how normal production quality plastic is affected, anything that disturbs the composition of the plastic being tested is probably unwise. 

Heating above the glass point disturbs the molecular structure and will invalidate what we are trying to observe.  Also, immersion is problematic because removing four samples of bundled filament of all water droplets that will adhere to the part must be done using an identical method - blasts of compressed air is probably the best way, but doing it exactly the same on four samples will be difficult to control.  In a 100% humidity chamber, especially at condensing levels, the same problem exists. A controlled 50% or even 80% non-condensing environment would be best.  This can be achieved using salts in the moisture producing water bath.  A saturated Sodium Chloride solution achieves a 75% humidity level at room temperatures.  Common table salt is readily available.

The starting state of absorbed moisture is not relevant to a drying test as long as all samples used are from the same source.  What we want to know is how well the drying methods work to remove moisture, and for that all we need to know is that the plastic has had adequate contact with moisture and is likely saturated.  A separate test for absorption rates is a better idea, and will be served by knowing how well each drying methods works. 

Prepare a sealed chamber with a platform to hold all of the samples above a volume of salt saturated water solution. A stainless steel mesh platform, or hold the solution in a separate open container inside the chamber;  so all surfaces of the samples are exposed to the vapor in the chamber. 

Place the chamber somewhere safe for a period of time, at ambient. It's my opinion 30 days is nominal based on many published reports of absorption rates. Optionally, the chamber could be placed into a dryer operating at 50c to accelerate the wetting process. An NaCl solution maintains 74% humidity at 50c, though adequate salt will be needed to ensure saturation is maintained.  In all cases, salt crystals forming in the solution should probably be removed or agitated back into solution.

The beauty of this 75% humidity method is samples can be removed, immediately measured, and returned before any ambient air conditions change the absorbed moisture content; and others making the same measurement can correlate under virtually identical conditions.

After the wetting period, measure the four samples for weight. 

Sample 1, Wet:___,  Sample 2, Wet:___ ...

Place each sample in one of the four test conditions. Begin the drying procedures.  

At some time interval, remove each sample long enough to weigh.  1 hour intervals would be great, but 2 hour intervals probably enough.

S1 Wet:____  2 hrs:____    4hrs:____   6hrs:____  8hrs:____  12hrs:____  24hrs:____  48hrs:____   (ambient)
S2 Wet:____  2 hrs:____    4hrs:____   6hrs:____  8hrs:____  12hrs:____  24hrs:____  48hrs:____   (dryer @ 50c)
S3 Wet:____  2 hrs:____    4hrs:____   6hrs:____  8hrs:____  12hrs:____  24hrs:____  48hrs:____   (vacuum @ 23c)
S4 Wet:____  2 hrs:____    4hrs:____   6hrs:____  8hrs:____  12hrs:____  24hrs:____  48hrs:____   (vacuum @ 50c)

After 48 hours drying, it is reasonable to expect the samples to be as dry as our testing needs to achieve.     Measurements can now be analyzed and compared.

Plus, once it is known, the best drying method can be used to prepare samples for the moisture absorption test.  48 hours in the best "dryer" environment is a reasonable approximation of "fully dry" material.  Again, moisture is absorbed.  It migrates from the surface of a material into the material. The rate is effectively unknown to us, so we should assume it is a slow process.  And we know plastic that holds water, like a coffee cup, isn't like a sponge: the absorption takes time.  And then the obvious, different plastics absorb at different rates: what works well for one plastic may not work as well for another.

ps: my current test using printed parts as the test sample is ongoing; but I still have condensing humidity after 7 days.  So I can't really remove and weigh my samples.  I may abort the test and restart using the salted water idea.  It just sounds more reliable from a weighing accuracy perspective -- I worry about a single hidden droplet of water on the part exterior invalidating the entire experiment.

RE: Drying Times and Temps in Dehydrator

Great post.  I'll need to absorb the detail.  Off the top of my head:

- I also had issues with condensation in my Humidity Box and was surprised at how quickly these sames (and the ones in water) lost weight when they were put in air (which may confirm your comments about it just being surface water). 

- I like have a single temp for the Dryer as all the samples can be done and measured at the same time. 

- I'm not sure on how to control the temp on the vacuum as chances are if I do that part in late Jan (after say 1mth of absorption) then it could be a 20c or 40c day for us and I'd not want to run the pump inside due to the oil vapour.  

- I still like the concept of drying the samples first, each roll has sat in my dry cabinet for different times (up to a year) and will have different starting points.  At least this way I'll know if the weight does not change then the Dry Cab works (but no statement on time), and it should give an initial level point to see how much moisture they gain over a month.  I'm not sure there is a downside to not doing an initial dry.

Thanks

Nathan

RE: Drying Times and Temps in Dehydrator

....and what filaments?  How about PLA, PETG, ePA-CF to start with?  or add others?

...& it looks like I'll take 35m of each filament that will give around 100g (according to prusa slicer anyway) as it will be easier to measure distance rather than weight straight off a spool.

RE: Drying Times and Temps in Dehydrator

Starting moisture, as in filament fresh off a spool, won't matter as long as all samples come from that one spool.  Drying before placing the samples in a wet environment will have little effect on the test outcome; it will just take a few hours longer to saturate the filament.  Key point here: One Spool; Four samples.   

As for heating the vacuum chamber, didn't I read where you heated the chamber to 40c?  This variant is only to judge how much combining heat and vacuum affects efficiency, and we already know based on commercial equipment, it's probably significant.  

50 grams is probably enough mass for your test samples, there's no need burning half a spool or $20 worth of filament for this.  Though 100 gram segments are still quite usable.

RE: Drying Times and Temps in Dehydrator

So I now have 4 x 50gm (ish) samples of PLA, PETG, ePA-CF all for the same spools so we can see how all variants of drying methods go.  I've had to use small zip ties to hold the bundles together.  The other option is tie wire but it may rust though in a month in high humidity.  The two zip ties on each bundle weigh 0.54g.  I'm glad with the 50gm suggestion as these were hard enough to wind up to fit on the scale (especially the ePA-CF as it is not very flexible).  

I'm away for a couple of days with work so will look at the Humidity Box, but how about just using the environment?  Here is what it looks like for Sydney over the last year at my place and we are in our Hot and Humid time of the year (while it varies, the average is going to be around 75%) + I'll be away for much of Jan and would not be able to monitor or maintain a humidity box. 

Thanks

Nathan

PS - On the other samples, the ePA-CF in both the Vac and Dry Cab is still not down to 0, they are both dropping but slowly.  

RE: Drying Times and Temps in Dehydrator

A humidity chamber is easy to make.   If you have a large plastic food storage container with lid, even your vacuum chamber will work well. 

Find a glass jar (or coffee cup), fill with 8 ounces hot water, add salt until it won't dissolve any more.   8 ounces of water needs a bit more than 2 ounces of salt.  Place the jar into the chamber, add parts around it. Seal chamber.  It requires no maintenance - the salt water evaporates as needed to keep the chamber at 75% RH.   

But - if your region stays around 75%-80% plus and never drops below 70% - outdoors is probably okay.  But is hard to replicate.  

RE: Drying Times and Temps in Dehydrator

Oh - and doing the math - if those cable ties are nylon, and 1 gram each, they'll add a 75% error to your measurements. 

• 50 grams PLA absorbing 0.8% water = 0.4 grams added weight
•   3 grams Nylon adding 10.0%  water = 0.3 grams added weight.

You'll want to add 3 cable ties to the humidity box to subtract the error.  Those you need to measure before and after, too.

RE: Drying Times and Temps in Dehydrator

I too have been thinking on the zip ties.  I "presume" they are nylon and the weight of the two zip ties on each 50g (ish) bundle is only 0.54gs but still....  I've got back last night and started to test a humidity box setup for stability and it is not too bad, but the box I'm using is way to big and awkward, so I'm going to pick up something smaller today.  At the same time I'm going to get some metal ties for the bundles and remove the Zip Ties before I start the hydration part (I've already dried the bundles for 5hrs @ 50c then left them in my dry cab for the last few days).

On a side note on my old samples I'm still taking measurements.  The ePA-CF in the dry cab is still slowing drying down (now down to 0.12%) which is encouraging for a long term storage soln.  The one in the Vac Chamber is fascinating.  I left it for a couple of days in vac and it not only stopped drying but gained some weight (went from 0.72% to 0.84%).  I gave it some hits this morning and dropped both times.  I don't think my cheap pump will like running all the time for long, so I'm to rig up a timer and run it on a schedule to see what happens over a few hours. 

RE: Drying Times and Temps in Dehydrator

I've got the humidity box up and going - stable so far at 85% (according to my cheap digital temp/hum scale anyway).  I've now replaced the zip ties with galvanised metal ties (adds less than 0.5g to the weight of each bundle, but if needed I can cut them off at the end and weigh each one to deduct from the total bundle weight.... but their weight should not change during the experiment like the zip ties would).  So, the plan is:

- tomorrow morning, measure all the bungles then put into the box

- take measurements each hr for the first 8hrs or so to see how the initial moisture take-up goes (esp on the ePA-CF)

- take measurements each morning after that till I go on Holidays 

- take final measurement when I get back.

How does that sound?

Thanks

Nathan

RE: Drying Times and Temps in Dehydrator

The first 8 Hours are done, and here are the average gains for PLA, PETG, and ePA-CF:

Some things to note:  I found that when opening the lid every hour, the RH drops quickly and it recovers slowly.  I eventually worked out that adding a little more hot salty water when resealing the box brings it back to 80%+ pretty quickly.  You can see the impact of this in the graph but it did give another insight to storage:

- Moisture Gain Propensity by Filament Type: ePA-CF absorbed twice as much moisture than PLA which in turn absorbed twice as much as PETG

- Moisture Gain Propensity by RH Level: All the filaments absorbed moisture twice as fast at 80% than at 60%

- What is the Target Humidity For Printing (eg when would a filament be considered too "Wet").  I've seen specs for Nylon (PA) that state 0.1% / 0.2% but that was for manufacturing.  Not sure what the target should be for FDM but at 8hrs my ePA-CF samples are already at 0.6%

Measurements from now on will be on a daily basis.

Thanks

Nathan

RE: Drying Times and Temps in Dehydrator

@tim-m30

I apologize for hijacking this thread but i'm too new to PM. I have a question about a post you made last month in regards to an issue with the Power panic circuit on the Einsy. If you have a moment would you get in touch?

Thanks,

Etienne

RE: Drying Times and Temps in Dehydrator

The Humidity Box is working well, keeping RH in the 75-80% range.  Here is the results after a week:

- ePA-CF: 3.5% and still gaining moisture

- PLA: 0.53% and has been at this for the last 3 days

- PETG: 0.39% and has been at this for the last 2 days

Merry Christmas!

Nathan

A side benefit

The dehydrator came in handy when near record rains overcame one of my outdoor security cams with moisture despite its water tight seals.

Disassembled the camera. Put into dehydrator at 158F for two hours got it nicely dried out. Some fresh silica packs, silicone dive grease on the gaskets later she was back in service.

It's not just for filament!

RE: Drying Times and Temps in Dehydrator

After 2 weeks, the ePA-CF is still gaining (but rate of change is slowing down).  I'll be away for a few weeks now but expect they will all be fully saturated by the time I'm back.  Then we can start on the drying experiments!

RE: Drying Times and Temps in Dehydrator

Posted by: @jmone

After 2 weeks, the ePA-CF is still gaining (but rate of change is slowing down).  I'll be away for a few weeks now but expect they will all be fully saturated by the time I'm back.  Then we can start on the drying experiments!

Thanks for putting in all the time on this. I am surprised that PETG seems to be absorbing less than PLA. I've had the most swings in print quality before and after drying with PETG so expected it to be much more thirsty!