Greetings all,
A recent rabbit hole I jumped into was things filament drying. Running 2 single spool heat dryers, and having many digital hygrometers & vacuum bags, it was time for some testing. Well, the heat dryers did the best they could, dropping their humidity by 20-25%. That’s room humidity, say 50%, the best the dryers could do was to 25-30%. Drying times exceeded 24 hours to acheive these results. Obviously, the last 12 or so hours had the least change. Actually, room humidity had more control. Starting the drying during rainy weather (60+% humidity) and ending on a clear, dry day (40% humidity) caused dryer results of 20% filament. Reverse these days conditions and the filament came out at 40% with 24 hour drying cycle.
This discovery created a need for an improved method.
Enter desiccant, the silica bead type. Starting with the packet style, it’s tough to tell how used they are and when to dry them. Since I wasn’t happy with the heated chanber method, it was time to deep dive microwave drying. The packets proved difficult to dry. The method used is low power settings over a longer time period. My idea was, heat the moisture to boiling point and have the oven force the humid air out. The packets provided a problem in absorbing and holding the humidity. When the temp dropped, the silica re-absorbed the moisture. Solution was to remove the beads and place them in a pyrex pie plate. Since heating water molecules is how microwave ovens work, air exchange would be critical inside the oven. Theoretically, only moisture adjacent items get hot. So I thought, when the beads are cool during heating, their moisture is gone. This lacks the reality that the beads don’t cool quickly and the now hot humidity doesn’t transfer to other items. Doh ! Lol. Like the heat dryers, removing the last moisture takes the longest wirhout more measures. The cooling process would require a sealed container as to reduce moisture absorption.
The cycle becomes, heat, cool in container, reheat until the beads heat only to the oven’s plate temp. An infraed thermometer works well here.
With beads dried, it was time to print some pla vented bottles & caps and loading funnel. At 3 per storage bag and the bottles holding, with room to move, the same amount of beads as a packet.
So, I have the heat dryer filament spool (cardboard) and a vacuum bag containing 3 desiccant bottles, a disc & a hygrometer. The disc was printed with a center hole and an x pattern cutout on one side using a smooth build plate. The disc is placed under the vacuum valve, smooth side up to allow the air to be pulled thru the x channels & up the center hole. This eliminates the vacuum pump’s down pressure sealing the valve from the contained air. Disc diameter to be wider than the valve and the pump seal. Works great.
To another suprise, one sealed bag was vacuumed tight, another sealed, but not vacuumed. Both hygrometers reading the same at 30%. A day later, the tight sealed bag showed no change in humidity while the non-vacuumed bag showed a 10% drop to 20%. I now have petg filament stored sub 10% RH as that’s the lowest reading on these digital hygrometers.
Hypothesized conclusions: starting with the filament mfg method of cooling extruded filament thru a water bath, we know why drying is necessary. What measures are done during mfg are, also, likely effected by that packaging day’s weather. Bags are vacuumed sealed with a desiccant pack tossed inside the center spool hole. While it may take several days/weeks to be opened by us, the vacuuming deters further drying by the desiccant. Especially with plastic spools. Having seen filament fresh from the bag having above 50% RH, the filament & desiccant pack needed drying. The quickest way to dry is 2 staged. Use the heat dryer to less than 30% RH, transfer to sealed bag with desiccant for 24/48 hours, replace desiccant and vacuum seal to remove air without over tightening the bag around the spool.
For me, the next steps are to print a soup can lid to use as a desiccant cooling container for microwave drying.
Make a sealed desiccant dryer box which holds much in freed beads.
Make a heat dryer attachment which cycles air to a condensor and back for rapid drying. The condensor will be an aluminum can to accumulate condensation created by ice water inside the can. Should be fun retirement activity.
Thru this deep dive, I now open all new filament bags and desiccant dry them in sealed, unvacuumed bags, changing the bottles until hygrometer shows dried. Long term storage is in vacuum bags with 1 bottle and properly tightened.