silica fabric windscreen

Where does the line start? Twisting up into a puck in the bottom of the pot is genius!

Hum — free-standing? Works on sheet rock? Interesting!
How long does the fabric stay stiff enough to keep its shape?

Cheers

"How long does the fabric stay stiff enough to keep its shape?"

Roger, I'm not sure I understand your question. Do you mean how many packing and unpacking cycles before the fabric softens? Or how long would it keep its shape once erected for use around a stove?

I don't know how many packing and unpacking cycles the silica fabric would endure before it started to fuzz a bit and become less stiff. Many, I would guess. Right now, the fabric will stand on its own and hold its shape over time without any sagging. I've had the windscreen unfolded, in a cylinder, on a shelf for several days now and it hasn't sagged at all. The stiffness of this fabric is similar to midweight (~3 oz) cuben, or 6-8 oz heavy-tow (maybe 8k) plain weave carbon fiber fabric. I can roll it around on the floor without very much change in the shape, and it wants to spring back open when I fold it up.

Si02 is a very high-modulus fiber, and this fabric is "preshrunk", which means it has more short-range order (more "quartz-like"), and a higher modulus, than the more common amorphous silica fabrics.

Can you add a spring to the screen to make it pop up if the stiffness degrades? If you made one with the same diameter as the hoops and placed it on the inside instead of two loops. If the fabric was only attached at the top and botom, you could still adjust it.

Very interesting post Colin. You're always thinking outside the box and it's that kind of thinking that really moves UL forward. Keep us updated!

Ryan

Thanks for the info. All new to me and very interesting. I wrote everything down in case I start on a project where it applies.

Hi Colin

> how many packing and unpacking cycles before the fabric softens?
Yup. I would expect some fracturing of individual fibres with each folding – but I might be wrong. Life testing needed!

The free-standing bit is very nice.

Cheers

Roger, I have concerns about the brittleness of the silica fibers, too. I agree that some breakage of fibers from creasing is likely to happen. Folding and unfolding of the fabric only occurs several times per day during trips, and perhaps a hundred times in a year, and the fabric is never subject to any tensile load. So, hopefully fiber breakage and weakening of the fabric will occur slowly.

I think the basalt fiber fabric would probably suffer far less fiber breakage. It has mechanical properties similar to S-glass, and tolerates flexion very well.

Hi Colin

You know, you can get conveyor fabric for baking ovens etc. A combination of PTFE and glass, or silicone and glass. And it is designed to handle some flexing as it goes around rollers. Temp range -150 C to +260 C. I wonder how that would go?
See for instance Chemfab or
http://www.chemfab.com/uploadedFiles/SGchemfab/Documents/Top%2030%20Brochure%20English.pdf

Cheers

Roger, thanks for that link. One concern about a completely siliconized textile for a windscreen is flame exposure on the inside surface. My little alcohol stove occasionally has flare-ups that send flames up the sides of the pot a little bit. Even very refractory silicone like the Cotronics stuff might not withstand direct flame for very long. Also, most commercially available silicone-impregnated fabrics for high temperature applications are very heavy. I like my silica windscreen because it is lighter (and bigger) than the aluminum tooling foil windscreen I have been using.

Yeah, I think that would be a bit heavy.
I am wondering if just plain fiberglass might work. Most of the 6 and 9 oz cloths would be out because they have larger fiber sizes, hence could break if folded sharply. Even some of the 4oz is just looser woven, but the same grade. They do make a 3.2oz (varries a bit in this range) with finer fibers.

I have a bit left over from canoe building and will have to try it. The volan coating may burn off leaving it a bit brown, but shouldn't bother, otherwise.

I think baffeling can be accomplished with a simple spring like lower loop. It should just lift off the ground slightly, on one side.

It could be that a simple coating of silicone/mineral spirits around the bottom will let me spread the fibers, holding them in place, without having to cut them. If I have some caulk around that is any good, I can try that, too.

Nice idea, I like it. We hope it stands up after 10-20 uses. A side opening will cause a draft to blow the flame off to one side. Holes on bottom much better. Great idea using the epoxy silicone, I like.

Be sure to use a torch to fuse the ends of the fabric after sewing. You don't want those 1/8" long fibres sticking to the walls of your pot that might eventually stick to the walls of your stomach. I work with a lot of 6oz fiberglass cloth and I see how the fibers get every where. Have sun light reflect off your cutting board so you can see the millions of tiny fibers stuck to it.

Hi Jim

> I think that would be a bit heavy.
Dunno. I got some samples from Dotmar in Australia, and they were quite light. Chemfab start at 130 gsm and go upwards.

Cheers

Dunno. I got some samples from Dotmar in Australia, and they were quite light. Chemfab start at 130 gsm and go upwards.
Yeah, that *is* light.
Thanks!

OK. The fiberglass did NOT work. it had trouble supporting itself at 8" high. NOT a good idea.

Yes, that was my experience with fiberglass, too (both E and S types).

Roger, 130gsm is pretty light. Thanks for that tip. I've been considering trying to make a material like that. I have various fiberglass, kevlar, kevlar/PBI, kevlar/carbon, and carbon fabrics in the 1-4oz weight range that I could impregnate with silicone using my 12" x 24" screw press. I don't know if the silicone would cure in the press, though. I might need a bleeder layer to allow volatiles to escape. I still have some concerns about exposure of the silicone to flame, but it might be worth a try.

A while ago, I have accidentally found an interesting material that might work well in this application. It is sold as a reusable baking paper, it is a thin teflon foil with some loosely weaved fibers in it. I weighted the piece I have (i bought it without any particular use in mind, so far I found it very useful for ironing a seam tape onto a fabrics), it is 140g/m2 what seems lighter than metal foil windscreens. The hoops will be needed, but the material is stiff enough to stand without any vertical supports. I like the idea of folding a windscreen this way, I may give it a try if I find some light but springy wire.

Hi Colin

Not many silicones have volatiles. It is usually a polymerisation process, often using moisture from the air as a catalyst.

Cheers

Hi Jan

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

But sometimes you can use humble copper wire instead. Yes, it bends, but you can straighten it many times.

Cheers

"Hi Colin

Not many silicones have volatiles. It is usually a polymerisation process, often using moisture from the air as a catalyst.

Cheers"

Most RTV silicones are acetoxy-cure and put off acetic acid as they cure, which is catalyzed by moisture (as you mention).

There are other curing systems though, like 2-part platinum-catalyzed systems and 1-part oxime cures. Silicone is fun!

Roger and Brad, thanks for the information about curing of silicones. Will a thin layer of silicone cure if it is pressed tightly between two sheets of plastic? If I want to spread silicone on a piece of fabric, then force it into the fibers with my screw press and cure it under pressure between sheets of LDPE film, should I very slightly dampen the fabric first? Or should I just leave the piece exposed to humid air for a few minutes after painting the silicone onto it, then put it in the press?

Assuming your silicone is typical RTV stuff, the following will be true:
-The thinner the layer, the faster it will cure
-Access to atmospheric humidity drives the curing (20-50%ish RH), liquid water not quite
-Heat won't help

Since you're working with such a thin layer, it might cure pretty well in just about any condition. If you can put it in a jar or something with some wet paper towels to up the RH, that could help too.

Why do you need to clamp the part while it dries? Once impregnated, the silicone probably won't run out of the fabric, especially since it will "skin over" quickly as the outside cures (a few minutes max.).

Oh, and I guess I didn't mention it, but your windscreen is great. Awesome use of materials, and the rubber holes are very inventive.

Hi Colin

> Will a thin layer of silicone cure if it is pressed tightly between two sheets of plastic?
Do it on a humid day. Breathe on the LDPE sheets. By the time you have spread the silicone out to a thin layer and clamped it flat, the process should be well under way.

Yeah, silicones can be fun.

Cheers