|Posted on Sunday, October 26, 2014 - 09:40 am: ||
I've been researching and experimenting with pourable silicone, thinking it likely has a variety of handy uses...
The official stuff is a two part epoxy for like $30 a quart. Not bad in the whole scope of things, but it is expensive, hard to get, needs to be custom ordered, and it has a finite shelf life. There are also pourable polyurathane two part epoxies that would also be incredibly useful for a lot of different things.
Meanwhile though, to the garage hobbyist, I was looking for a cheaper and lower barrier to entry alternative.
A little googling showed some good results.
I am working with silicone II, because it is not so acidic like normal silicone. Ultimately I want to use it to try and pot electronics. You can get a caulk tube worth of it for a few bucks.
I thinned it with "Mineral Spirits", because I had them on the shelf already. Xyelene was also recommended, I don't know if mineral spirits and xylene are the substantially the same thing.
It worked. The resulting silicone poured beautifully, though I have read that it will shrink in proportion to the amount of thinner added (which makes sense).
The next obstacle is to get the thicker pours to cure. By itself, it will take a thick goo of silicone a month to cure (literally).
People are solving that three ways, by mixing in a bit of acrylic paint, by mixing in corn starch, and by mixing in talc. I used anti monkey butt powder (talc with some other stuff), again, because I had it on the shelf. It seems to have worked, I poured a captive 3/4" thick plug in a shaft just to see what it would do, and about 8 hours later it was already more than half set up.
The other approach I found was to "water whip" the silicone. They said to use a wire wisk, add water to the mix (which won't mix), and whip it for a bit. Silicone is water cured, so that activates the whole mess. Then drain the water and apply the silicone.
Heat is also supposed to speed up curing as well.
I'm thinking of trying a mix of the two, and making a corn starch / talc and water paste and mixing that in.
The next thing that would be fun to try (if I can get thick pours to set in a reasonable timeframe) would be to fill the "open space" in the front Uly motor mount with a silicone pour... to either preserve the origional polyurathane in there, or reinforce it, or to just change it's characteristics. With the right durometer pourable polyurathane epoxy, you could even completely rebuild that front isolator. The metal parts don't wear, and given the stupid high prices for replacements, that might be a viable option. If Harley stops selling them, it may become a necessary option.
Anyway, more to come as I experiment more. Anyone feel free to chime in if they have questions or answers... I didn't have any chemistry beyond two years in high school, so I am a bit out of my depth here.
(Message edited by reepicheep on October 26, 2014)
|Posted on Friday, November 07, 2014 - 10:03 am: ||
As an update on this...
The first try worked better than the second one. Silicone II (which I am using because I want the option to pot electronics, and it appears a better choice because it is less acidic) with talc powder (anti-monkey butt powder was what I had on hand) mixed dry and mineral spirits worked quite well.
It will still take a while to dry, so if you pour it 1/2 inch or an inch thick, it may take a week or two to cure. And it will shrink while it cures by the ratio of mineral spirits added, so if you do 1:1 to get a really easy pour, expect it to shrink to half the material. And it will be greasy and smelly while it cures (but then seems to clean up nicely). The result seems *very* strong, and it sticks like stink. At least as well as normal silicone, maybe better. And it didn't pull away from the walls of a cylinder while shrinking and curing, it just stretched. So it looks pretty useful for a lot of purposes, I'll try potting some electronics next.
The second attempt with silicone II and a water and corn starch paste did not work very well. I hoped the wet corn starch would accelerate the cure. It didn't seem too, and the resulting silicone almost became a "chalky silicone". I don't know if it was a result of corn starch, or as a result of the paste instead of the powder, or as a result of so much water in the mix.
Next steps? Acryllic paint has been mentioned as a good mix to accelerate cure, I may try that with the talc and mineral spirits. It would make a nice colorant as well, and apparently you don't need much of it to speed up the cure.
I'll also try a less aggressive thining of the mix by using less mineral spirits, and maybe try and find some Xyelene and see if that works better. My mix was super thin and poured really nicely, but it could be a lot thicker and still work fine.
Maybe I'll try some small batches with some other even more insanely volatile solvents, like contact cleaner or brake parts cleaner.
|Posted on Saturday, April 25, 2015 - 09:43 am: ||
Try baking soda in place of the powder.
|Posted on Sunday, April 26, 2015 - 10:06 am: ||
I want to use this to pot electronics, so I'm worried about anything too far at either end of the basic / acidic range. Ill try it next time though.