Stirlingengineforum.com

I'm not sure I'm looking at the right stuff, but "paper clay" just seems to be wet paper and glue? That might be light weight, but I doubt fireproof.

Anyway, I realized, after looking into it more, that years ago, fooling around with air crete, I was probably just using some mortar mix I had left over, which at the time, some air crete formula included sand, but I see lately many people now use pure Portland cement for what looks like really lightweight cement foam.

I'm basically looking for something that would be a "drop in replacement" for the foam displacers in readily available "coffee cup" type LTD engines

If I can find something that works really well, I might offer a kind of "upgrade kit" for converting an LTD to high temperature

I've seen a number of comments from people on YouTube as well who simply tried running their LTD on a candle and completely ruined the engine by melting the foam displacer.

I haven't had time to try all the ideas and materials proposed so far. Still working on setting up the workshop.

Out of curiosity, have you tried the type of fiberglass circuitboards are made from? Those are definitely fireproof: They have to survive all kinds of high temperature processes. Or is that too heavy?

Also, you can get unimpregnated carbon cloth from here: https://www.grs.ie/product/carbon-fibre/

I'd imagine there's similar stockists in the US. I assume you have high temperature epoxy you want to stiffen it with?

Thanks for the tips! I did not consider circuit board material.

As far as stiffening the carbon fiber cloth, though I think it is fairly rigid-ish to begin with, some water glass / sodium silicate, sprayed on and baked in a kiln would probably do the trick without adding a whole lot of weight.

What I'm working towards lately is something that can survive the high temperature heat of a hydrogen flame, which can approach about 4000°F.

I don't think high temperature epoxy will suffice for that.

The hot end cap might need to be made of tungsten or something.

Unfortunately, it seems that source for carbon fiber cloth does not ship outside Ireland. At least there is no other option in their online order form.

I can always use the carbon fiber board I have and just heat it up enough to burn off the resin, but.. if it could be avoided, that would be better.

Carbon fiber cloth isn't very rigid, it's similar to fiberglass cloth if you've ever worked with that. Maybe similar to very heavy canvas if you haven't. Either way it doesn't have any rigidity until the epoxy cures.

I've never tried stiffening fabric with waterglass before, but if it adheres well to glass then it might work. Keep in mind the resulting product might be less flexible/more brittle though.

Here's a few US sites that stock carbon fiber fabric. In general any place that stocks fiberglass supplies for boat maintainence will probably have it.

https://www.carbonfiberglass.com/compos ... ber-Fabric

https://www.jamestowndistributors.com/p ... %2520Cloth

https://fiberglasswarehouse.com/collect ... rbon-fiber

Just so I can get a picture btw, what are you trying to achieve with this? In the engines I've seen up to now the displacer is never in direct contact with the flame. Does the final part need to be particularly strong? Or just light? If the latter there might be cheaper solutions than carbon fiber.

pehoulihan@gmail.com wrote: ↑Mon Apr 11, 2022 12:34 pm Just so I can get a picture btw, what are you trying to achieve with this? In the engines I've seen up to now the displacer is never in direct contact with the flame. Does the final part need to be particularly strong? Or just light? If the latter there might be cheaper solutions than carbon fiber.

Ideally, light and strong and fireproof. (And non-heat conducting)

I've got a rather wide variety of applications in mind.

Most LTD style Stirling engines are designed to run on a cup of warm water. Temperatures much above that and the plastic & foam start to warp and melt. But I think the same design would work well as a stove fan, or wood stove top generator.

Many wood stoves have a removable lid a larger size LTD style engine could go over.

Of course the engine would be high temperature, but of the traditionally "low temperature" profile.

It shouldn't be so delicate it can't be left in the stove, or might burn up if the stove got extra hot, as they tend to do sometimes.

The typical Peltier type stove fan can't take much overheating. I had a friend who went through several, despite the bimetal "safety device" and sitting off to the side on the coldest part of the stove.

Ok, I see what you're getting at. I'm thinking maybe two layers of thin circuitboard FRP (you can get it in different thicknesses) with something lighter sandwiched in between. Probably mix up glass spheres with high-temp epoxy for the filler in the middle. It's very light and very easy to machine. you can get the spheres from pretty much anyone who sells epoxy.

I might try it, though I'm skeptical about anything epoxy holding up under very high temperatures.

Recently I discovered microwave ovens have mica sheets to cover the magnetron. The same material the heating element in a toaster or hair dryer are wrapped around.

If it can stand repeated direct contact with a red hot heating element without burning or giving off toxic fumes, it could likely work.

The mica wave guide cover material can be ordered in "cut to size" sheets for microwave oven repair, and seems relatively cheap, compared with natural mica anyway.

https://youtu.be/WsK6J2rxOVQ

I think I found what I need.

It might be time for a new toaster:

Although it is apparently the same thing, I was able to find larger size sheets in various thicknesses, 0.2mm up to 10mm, (1mm or 1.5mm or less, should be plenty thick enough for most small engines I think) and much less expensive searching under mica + toaster rather than microwave, for some reason

Listed as "mica heat resistant insulation" on eBay, if you don't want to sacrifice an old toaster, heck, there are four fairly good size sheets in a new cheap $10 toaster.

Interesting find, how strong is it? I was under the impression mica is brittle.

Circuitboard FRP is definitely heatproof enough for any temperatures you're likely to create with a regular wood fire. It's designed to be able to withstand repeated heating and cooling with a gas soldering torch.

Natural mica can be brittle and separate in layers, However, I just found, last night after posting, that the microwave in my kitchen I've been using for years has such a panel I never noticed before. I took it out and it seemed very rigid and quite strong, infact difficult to bend to get out from under the tabs, almost like metal, but actually more rigid and more difficult to deform than metal, can't bend permanently, until it breaks anyway.

What is FRP exactly anyway. I can't seem to find any as blanks, just old circuit boards with all the electronics.

I found "Red Bakelite Phenolic Resin Flat Plate Sheet PCB Selected Size" on eBay

Phenolic resin will burn over 1000°F or so and is apparently relatively low toxicity, considered fire safe in public spaces, office buildings, airplanes etc. where fire safety is a concern. So, probably OK for my Brent Van Arsdell Limited Edition restoration project, though I wanted something that looks "antique" for that.

As I mentioned, I'm also looking for displacer material for high temperature engines where it seems likely that at times, the displacer itself may get glowing red or even white hot.

Various refractory materials seem ok but tend to crack and break up over time.

Right now, the most promising material I've been working on has been foamed porcelain, possibly with some glass microspheres, though they just seem to melt and collapse under firing.

Right now I'm researching glass foaming agents. My thought is to use a foaming agents, basically baking soda and vinegar (sodium acetate).

Instead of trying to add glass spheres to the clay before firing, the sodium acetate should react and form gas bubbles from inside the clay during firing. The same way cellular glass is made, which I've been looking into, but seems difficult to get. Ceramics can also take more heat than glass. Another advantage of ceramic is there is no limit to how it can be shaped and formed. If I can figure out a good formula and the right firing sequence.

It seems the foam, once formed during the firing process needs to be cooled a little fairly quickly to prevent the bubbles from collapsing, but then cooled gradually the rest of the way to prevent cracking.

I think I may run a generator to power the kiln for such experiments as the commercial rates for electricity around here are ridiculous, or I might need to get a small (and or large) gas fired kiln.

Maybe just mix the porcelain clay with vermiculite.

About FRP:

...an FRP reinforcement, which technically speaking is fiberglass impregnated with resin. Thus, it does the job of holding the layers together to achieve a desired thickness of the PCB board. It is mainly responsible for the correct binding of layers, the insulation between them, and also for reducing the overall weight.

https://absolutepcbassembly.com/what-ex ... -in-a-pcb/

That's about all I've been able to find. I haven't yet located a source specifically advertising circuit board material as FRP.