Materials question: adaptable gasket

September 6, 2020 10:56 PM

I need some soft rubber or silicone tubing -- think like a bicycle inner tube, but maybe half the diameter. I need to be able to fill it with some kind of gel and then permanently seal it into a torus. It's going to function as a sort of adaptable gasket that conforms to a variety of surface shapes within a set of tolerances. Where can I get tubing like this, what kind of gel should I fill it with, and how do I seal it? Bonus points if it's skin/body-safe.

N.B.: I have already explored silicone ostomy gaskets as an alternative solution, but I want to prototype this sealed-ring idea and see if it works better.

posted by cnidaria to Technology (8 answers total)

There are inner tubes available for all sorts of wheel sizes available. Both bike trailers and kids' bikes inner tubes are easily available and cheap, have smaller diameter wheels, and might fit your project?
posted by Harald74 at 12:02 AM on September 7, 2020 [2 favorites]

Best answer: The need for something to fill the tube with to hold an adaptable shape reminds me of the infamous recalled "Stretch Armstrong" doll/action figures from the '70s. They were filled with gelled, dehydrated corn syrup. You can search for "stretch armstong filling" to find more detailed ingredients lists.
posted by Larry David Syndrome at 5:05 AM on September 7, 2020

Sand might work or also thermoplastic if its ok for it to set hard in its rubber sheath.
posted by J.R. Hartley at 5:20 AM on September 7, 2020

You could use an innertube. You could cut it to length and patch it together (allowing for some overlap). Some presta-valve innertubes have removable valve cores specifically for injecting sealant into the tube; filling the whole tube that way would be tedious, but should be possible. Innertubes are available in butyl rubber, (less commonly) latex, and (much less commonly) thermoplastic. Latex is somewhat porous.
posted by adamrice at 6:31 AM on September 7, 2020

Best answer: This is probably going to take some trial and error, but Polyethylene Glycol is thick and food safe. Viscosity goes up with molecular weight, so I'd guess PEG 400 or 600 might work. There are an outrageous variety of rubber tubing materials out there, so maybe peruse McMaster.com and see what fits your size and needs. It may be difficult to find an adhesive that works well with silicone. Sealing the filled tubing sounds difficult, off the top of my head I'd consider a small length of smaller diameter tubing that inserts into the loop of larger diameter tubing to bridge the gap and support the seam for gluing. McMaster also has adhesives of all types, and a somewhat more limited selection of food-grade adhesives.

Good Luck!
posted by Dmenet at 9:36 AM on September 7, 2020

Seems like what you're describing is an o-ring, and those are available in large sizes and a variety of materials. Here's a 12" in silicone.
posted by bricoleur at 9:53 AM on September 7, 2020

Best answer: A couple of not-so-easy ideas (think I saw it in a cartoon once):

DIY rotational mold your own inner tube. Use a soft mold making RTV for the cast. I recently bought TAP Plastic's Urethane RTV (30 A, rubber band soft) and FiberGlast's 60 Shore A Casting Urethane for a tiny casting project using a 3D printed mold. For a torus mold I'd consider using a Round Nose Router Bit to make mold halves from thick MDF (2x4 ft sheets usually available too, laminate for thicker). Paint the MDF to smooth & seal before casting. I've no clue what to fill it with.

Another thought is to shape the gel then coat it. In 2009 I bought 1/4" thick Ultra-Elastic Clear Gel Rubber (like under the cloth on a the gooey bicycle seat). Maybe cut to shape with a scissors, stack if required then and paint with Plasti Dip? I bought it from McMaster-Carr but they no longer carry it... they are helpful and may point you to another source. Their p/n was 1782T56 (was $40.89 for a 24x24" sheet). I thinks I tossed my leftovers last year as the surface got sticky.
posted by tinker at 10:03 AM on September 7, 2020

Best answer: Aquarium tubing (available at both specialty aquarium stores and most Home Depots and Lowe's type stores).
posted by WalkerWestridge at 12:07 PM on September 7, 2020