Make your own O-rings and tubing from silicone!
The object in this picture is a homemade submersible camera housing, made possible by the silicone O-rings. (my next instructable will be the camera housing)
Quick and dirty explanation: Inject silicone adhesive straight from the tube with a caulking gun into clear Vinyl tubing, let it cure, blow the silicone out with compressed air, cut the silicone to length, re-glue it to form rings. If you want tubing, blow out the silicone before it cures...
This instructable will not only show how to make the O-rings and tubing, but go into detail about the way silicone adhesive behaves so you can exploit it, and make even more things!
Step 1: Materials
The primary material is Silicone adhesive that comes in tubes for caulking guns.
1. THERE IS A DIFFERENCE AMONG SILICONE TYPES. DO NOT USE "Silicone II", it is not pure Silicone, and will not behave as predictably as "Silicone I" , (or 100% silicone). The black Silicone is from ACE and is my favorite. Clear GE Silicone 1 is great too.
2. Clear Vinyl tubing. This is what you will be pumping the silicone into, it's the mold for the O-ring and tubing. The "I.D." or inside diameter of the tubing will be the "O.D." of the Silicone O-ring you are making.
3. Masking tape, compressed air, sharp knife, high quality caulking gun, about a week of cure time.
Step 2: Inject the Silicone Into the Vinyl Tubing
Using the caulking gun to force the Silicone into the Vinyl tubing, squeeze away! You will notice that as the Vinyl tubing fills up with silicone, it will get harder and harder to fill, due to the high viscosity of the Silicone. It will take considerable pressure to hold the Vinyl tubing onto the tip of the caulking tube. (a nice caulking gun is worth the price here)
You may only be able to pump about 15 or so inches of silicone into the Vinyl before it just wont take anymore, and you will actually feel the Vinyl tubing expand from the pressure!
The tubing shown here has an I.D. of 1/4 inch, which is an amazingly convenient size. The only other size of tubing I've tried is 1/8 inch I.D., anything bigger than 1/4 inch I.D. will take some special care... but more about that in a minute.
Step 3: Optional : Make Hollow Tubing Instead of Solid Silicone
At this point the Vinyl tubing is filled with uncured Silicone, and you can keep it solid, or make tubing out of the silicone itself!
All that needs to be done is apply compressed air back into the Vinyl tubing, which will force the uncured Silicone to flow back out, while leaving enough of it stuck to the inside of the Vinyl, so that when it cures, it will be tubing!
If you use compressed air to do this, use the bare minimum amount of pressure. The reason is, after the silicone is forced out, the sudden blast of compressed air through the tubing will cause the thin film of uncured silicone stuck to the inside of the Vinyl to "Ripple" due to violent turbulence of the compressed air
Step 4: Waiting for the Silicone to Cure
Now comes the waiting... a little extra information while we wait for the cure:
The interesting thing about this method, is that the Vinyl tubing material, though waterproof and highly resilient, will not prevent the Silicone within from curing. The Vinyl does not make a good "vapor barrier" and therefore permits curing. Silicone cures from the outside in.
The (solid) Silicone if left in the 1/4" Vinyl tubing may take more than a week to cure. If anyone has ideas on how to speed up the cure< let me know.
The silicone that has been blown through to make hollow tubing, will take a single overnight, maybe more.
The difference is that the air can get to the inside of the tubing and help it cure faster.
Being the impatient person that I am, waiting is hard. The first few times I made these, I kept checking and checking. The Silicone that is near the ends of the Vinyl tubing will cure relatively quickly, even up to a half an inch of it will quickly cure due to its proximity to open air. Do not be fooled, the Silicone deep inside the Vinyl has a way to go yet.
You may want to make a few lengths of this tubing at once, if for no other reason that to test how the cure is coming along. Just cut a section of your test tubing, any others should be about the same.
If anyone uses Vinyl of more than 1/4 inch I.D. Let me know how it goes!!! (my prediction is a ridiculously long cure time...)
Step 5: De-molding the Silicone From the Vynil
Now comes the really really fun part! - Removing the cured Silicone from the Vinyl tubing!
There are two methods for doing this. The compressed air method works only on solid Silicone. It's as simple as it looks: Hook compressed air up to the Vinyl tubing and blow!
This method at first seems like it wouldn't work, after all, you cant push on a rope right? But what happens, is that the compressed air will cause the Vinyl to expand, and therefore separate from the cured Silicone within, leaving a slight gap... the compressed air will work it's way down the gap between the Silicone and the Vinyl, and create turbulence between them.
The sound of this happening is hard to describe, but sounds like pinching a latex balloon opening so that it squeaks loudly. The Silicone will shimmy its way out of the Vinyl without you having to do much except laugh at the simplicity of it all.
(This joy is similar to the joy experienced by the Flying Spaghetti Monster as it gives birth to spaghetti children... or so goes the legend anyway)
If your Silicone is still uncured, this whole thing will not work.
The second method of Silicone removal is to simply pull it out of the Vinyl by hand. Since the Silicone shrinks when you pull a piece of it length-wise, it will pull away from the inside wall of the Vinyl tubing, and come out. You will probably find other ways of doing this, i.e. with water, etc. If you use the "pull method" it helps to straighten out the Vinyl tubing.
Step 6: Cutting the O-rings to Size
From the Silicone that has emerged from the Vinyl, you now have material for your O-rings!
1.Cut the Silicone rubber "cord" to the desired size (circumference)
2. Make the cut ends as flat and uniform as possible.
The silicone "cord" is VERY flexible and soft: pre-stretching it (by making the O-ring slightly small) is very usefull here, if your O-ring is meant to hold snugly around something. The Silicone should stay soft and pliable for a looooong time, many years.
Step 7: Join the Ends to Make the Final O-ring
Basically, you're going to use the same Silicone adhesive that you made the O-rings with, to glue the ends together.
1. Using masking tape, wrap both ends of the cord. Doing this prevents the Silicone you use for the fusion, from getting onto the smooth surface of the O-ring.
2. Using a wider piece of tape as a cradle, position one end of the O-ring.
3. Glob some Silicone onto the other end of the cord
4. Push the ends together, then lock the tape down. There is actually just a tiny amount of silicone used to fuse the ends together!
5. Keep the taped ends Parallel to each other, the O-ring will be "round" don't worry!
6. Wait overnight for cure
Step 8: Remove Tape, You're Done!
Remove the tape, and clean up the extra silicone from the joint, which should be very easy, since the tape prevented the silicone at the joint from sticking to the O-ring. The joint will leave a little imperfection in the O-ring, but the Silicone is so pliable, it will not affect sealing performance.
Enjoy, and good luck!
(My next instructible will be how to make the submersible camera housing!)