silica fabric windscreen

[steven franchuk]

'> some light but springy wire.
You can often get 'piano wire' or 'music wire', which would do fine."

Colin used superelastic" nitinol (nickel-titanium alloy) wire. This is commonly called Memory Metal. This wire is manufactured into straight wire which sets the memory. You can bend straight wire into very tight loops and the wire will spring back straight. Nitinol will easily outperform Piano wire or music wire The superelastic alloy is I believe 56% Nickel and 44% Titanium.

"Can you add a spring to the screen to make it pop up if the stiffness degrades?"

Just stich two vertical nitinol wires between the nitinol hoops. If the fabric softens the vertical nitinol wires combined with the nitinol hoops would maintain the shape.

[James Marco]

"Just stich two vertical nitinol wires between the nitinol hoops. If the fabric softens the vertical nitinol wires combined with the nitinol hoops would maintain the shape."

Yeah, I had thought of that. Using the light framework, it becomes possible to use really light fiberglass. Some, .56oz/yard is thinner than silk, yet maintains fair integrity when curled down for packing. Siliconeized holes can still be cut, likely a little easier, too.

Weight should be about 3/4-1.5oz completed, depending on dimensions.

Great thoughts guys!!

[Colin Krusor]

I tried applying some of the blue Cotronics silicone to some kevlar and S-glass fabric scraps last night, but I wasn't able to effectively thin it. Mineral spirits has worked fine for me in the past for thinning silicone, but this stuff is not soluble in mineral spirits, apparently. I tried thinning it with acetone, xylene, and methanol, too, but none of those worked, either.

Any ideas? I ordered some toluene.

[Roger Caffin]

Yeah – pick a silicone which has a low viscosity, and use a roller. The cartridge stuff is non-slump, and a right pain.

Cheers

[James Marco]

Yeah if the xylene didn't work, I would not expect toluene to work. They are both the same family.
Try some plain lacquere thinner. I think this is a combination of three or four solvents that sort-of work together. I have some liquid rubber that does the same thing, it doesn't disolve at all with mineral spirits, and, only slightly with acetone…lacquere thinner works the best.

Actually, mineral spirits/WG doesn't really disolve silicone. It sort-of just mixes with it. Like mayonaise it forms a colloid with enough mixing.

[Colin Krusor]

Roger, I agree that a low-viscosity silicone would be much better for this, but I'd like to see if I can make the Cotronics stuff work because the actual maximum service temp is several hundred degrees higher than other "high-temp" silicones. In case of a flaming alcohol spill or stove flare-up, this stuff would be more likely to come out intact.

James, thanks for the tip about lacquer thinner. I looked up several brands of lacquer thinners, and the main ingredients seem to be toluene, xylene, and MEK. So, I think I might hold off on getting some for now and just try the toluene when it arrives. I used to have a can of Alvin Lab Solvent, which is mostly toluene (with some acetone), and I recall that it would dissolve things that were unaffected by xylene or acetone alone.

[Roger Caffin]

Hi Colin

I suspect the real problem is that the sot of solvents we often use are simply ineffective with the Coltronics silicone. Swapping between Xylene and toluene etc does not do very much.

Instead, try to get some light silicone oil or silicone solvent – hard to get but try Dow Corning. That may work where carbon-based solvents don't. (I forget the name of the stuff I used.)

Cheers

[Jerry Adams]

When using mineral spirits from Home Depot or Lowes, I have to stir it several times over a 15 minute period before it disolves completely. Until then, there are blobs of silicone in the solution.

[Colin Krusor]

Jerry, that has been my experience with thinning silicones with mineral spirits, too. It does take a while and a fair amount of mixing. This Cotronics stuff just doesn't dissolve at all, though. There are still blobs after a lot of mixing and several hours in the solvent.

Roger, I thought of that, too. I did some looking online for low molecular weight cyclomethicone oils that would evaporate readily. I might order some and try it.

[Colin Krusor]

I was able to lay my hands on a small bottle of cyclopentasiloxane (cyclomethicone) this evening, and I tried using it to thin the Cotronics silicone. Nothing. A completely undispersed glob of blue uncured silicone putty remained after a lot of mixing and resting at room temperature.

I'll consider sending an email to Cotronics, but I suspect they'll tell me what many silicone manufacturers seem to tell customers about thinning of silicones: nonpolar organic solvents sometimes work a little (depending on the silicone), and mixing with detergent-containing silicone-based commercial thinners works better, but these reduce the strength of the cured product. Given this, I think I'll try toluene and hexane some time this week, and accept that I can't thin this stuff if those don't work. I'll have to use another kind of silicone for thin coats on fabrics. I can still use the Cotronics stuff for "soft grommets".

[James Marco]

Try a blend of methylethylketone(MEK), toluene and acetone.
Have you tried water?
Anyway, the trick is to break or encapsulate the small molecules. You might also attempt slight thinning, say 5:1 with standard silicone. Alcohol might also work.
Running out of ideas, though… detergents, and even some solvents will effect the silicone, even if it appears to work, as you say.

[Colin Krusor]

Hexane works, it turns out. It is the least polar of the solvents I tried, so I guess I should have tried it first given the hydrophobicity of silicones. It takes a bit of mixing, like regular silicone and mineral spirits, but it eventually becomes a uniform mixture. Some time later in the week, when I find time, I'll try siliconizing some high temp fabric scraps.

[Roger Caffin]

Um …

Pretty sure water will NOT work at all. Most likely it will accelerate the curing.

MEK is a bit nasty: '143 volunteers exposed to 200 ppm for 4 hours reported throat irritation, unpleasant odour, nausea, and headache (in order of frequency reported). Higher exposures are expected to cause central nervous system depression with symptoms such as headache, nausea, dizziness, drowsiness, and confusion. Extremely high concentrations may cause loss of consciousness and possibly death.'
http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/mek/health_mek.html

Non-polar hexane – figures, and useful to know.

The silicone solvent I did use was Dow Corning OD-20 I think.

Cheers

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