Solution for printing with water soluble PVA in Dualstrusion

by robosavvy, published

Solution for printing with water soluble PVA in Dualstrusion by robosavvy Apr 10, 2013
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How to use PVA without it absorbing ambient moisture.
The filament is to be contained in a airtight connector that only exposes the filament to ambient moisture for a few seconds before it is extruded.

More information at: http://robosavvy.com/forum/viewtopic.php?p=37534#37534

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I've got this fully printed, and picked up a container, which isn't perfectly sealed. However, I also went out and picked up a gun safe heater (like 10w), and have a thermal controller ($20 for the controller). So I'm going to set it up as a thermal controlled unit. I'll upload pics shortly. And plan to put some desiccants in the box as well.



Basically all you need to do is hook power to the thermal controller and directly connect the heater to it. It will keep the temp to within a 1/2 degree.


A small heater inside (low watt light bulb) could help out, though it sounds like it's working nicely as-is. You'd have to keep the heat from warping the filament though, so it would probably mean a larger container is needed.

How well does it keep water out? Have you put a humidity gauge inside the box. Water vapor is one hellova difficult thing to fight against. My job deals with water vapor, and I can pretty much assure you that after a few hours your box's humidity will be equal to the outside humidity. Dessicant is absolutely useless as long as the container is not hermetically sealed or under positive pressure with a dry gas. Please dont think I am needlessly bashing your Idea. There is a big difference between this looks like it keeps water out, and this solution keeps water out.

Even a pinhole size hole can equilibrate an entire dry room in a matter of hours.

Hi sciencemike. Good to get some feed back from an expert.
Of course this system is only as good as the original container, how well you seal the spout with hot glue and the snug fit of the filament on the latex.
We do not have a humidity gauge, but what i can say is that usually a few hours exposed to atmosphere is enough for PVA to become softer, and harder to extrude.
I have a roll in this system for over a week now and it is still bone dry.
I assume whatever small leakage there is, is small enough for the desiccant bags inside to maintain a dry atmosphere.
Anyone who buys filament should have a steady supply of desiccant bags to reuse (just as long as they are stored in a airtight container so avoid becoming saturated with ambient moisture).
However we might have a need for a more professional system based on this so I will get a humidity gauge to do a more scientific approach.


I think sciencemike's solution should work just fine concerning the small leakage. He putted some desiccant packages in the container to remove moisture actively.

I like where you are going with the idea and yes the original seal on the box is very large and if it does not use an oring then that would be a pretty massive source of humid air. The problem you are trying to solve is one that desperately needs solving. So I wish you all the luck.

Grab a sensirion humidity module and plug it into one of your arduino boards, throw a small display outside the box and have it datalog or just remember highs and lows, that should be doable for under 30 $. Goodluck.

Very cool! I was thinking towards a way more specialized container (have the means to make some), but adapting an off the shelf part for it is way better. Is there any blocking rubber in the spout?

It's easy to add moisure absorbing pellets in here, either the consumer stuff or silica pellets.



The spout has a slight taper to grab the filament guide tube.
That part does not need a airtight fit. I am only concerned about not letting air into the container and the latex in the base of the cone is enough for that.

We have plenty of desiccant bags laying around. I placed a few in the container just to make sure. You can also reuse them if you have a temperature controlled oven.