Accommodative DIY Covid Respirator Mask: Flexible Casted Silicone from 3D Printed Mold

thingiverse

This is basically a proof of concept project. It did work out for the most part, but there are some significant challenges to overcome before the approach could be useful for making emergency respirators. My hope for the design I went with is that it can better accommodate a variety of face shapes and sizes. That's why it has a lip that flips over for where the mask meets the face rather than just an edge. You see this on most commercially made respirators. While you could print it out of rigid material like PLA and heat it up to form to the face, it's better to make it with flexible material. I haven't tried with flexible filament. Instead, I designed molds into which castable silicone can be injected. A big advantage of this approach is the potential for ramping up production as more molds are printed. Also, there may be some sanitary benefits to using silicone, particularly if you sand the molds to get rid of striations. The real shortcoming of this project is that hard silicone (Polytek Platsil 73-60 or Smooth-On Smooth-Sil 960) take too long to solidify enough to de-mold, probably even after speeding up the curing in an oven and using an agent. Plus they are prone to ripping when stretching off the mold core. I might try heating it up to prevent ripping. On the other end of things, soft silicone (Smooth-On Dragon Skin 10 NV) cures faster but isn't structural enough for a full shell, even after trying 4mm wall thickness and ribs. The solution I suppose is to have a semi rigid shell with just a soft silicone rim. The semi rigid shell could be molded with something like Task 8 as demonstrated by Smooth-On in a recent blog post. Here's a quick description of the files I've uploaded: - Accommodative Respirator: The whole project as developed in Rhino 5 - Mask Shell 2mm and 4mm: The shells you could 3D print directly but really are the approximate result intended by casting silicone - Mold Core for 2mm and 4mm wall thicknesses: The core of the mold which the shells will have to be pulled off of. - Mold Face: The mold face - Mold Outer: The outer portion of the mold which includes the receiver for the feed tube - Feed Tube: A tube that inserts into the Mold Outer into which you pour the silicone - Plunger: A plunger for speeding up the pouring of silicone into the mold - Locking Ring for 4mm Shell: A ring that sits inside the channel of the silicone shell that together with the next part sandwiches some filter material (could be glued to the silicone) - Face Plate for 4mm Shell: The face plate that snaps to the locking ring and has attachment points elastic straps. The mold parts are to be connected with some 4" - 3/8" bolts. Make sure to put some nuts in the traps inside the mold as these are needed to separate the mold after curing (by inserting bolts). You might want to use a de-molding agent to make things easier. Before de-molding, you'll also want to cut the cured silicone going from the feed tube to the shell via the channel (should be covered with tape when pouring the silicone). As far as what kind of elastics straps to use, I haven't figured that out yet. And I haven't thought too much about what to use for filters either. There are a lot of other respirator projects out there that get into this. I'd loved to get some input on this project. I'm especially interested to hear of any alternative casting materials that could work faster and hard at least 60 durometer but still flexible. @PercyFlores thought of using rotational molding is very promising as it doesn't require a core and so that mask could be pulled out of the mold much earlier in the molding process. Plus, only to molds have to be produced per set.