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Alphax wrote: ↑Thu Feb 10, 2022 5:19 pm
Weight of Titanium sheet 12" x 12" x 0.016" = 6 ounces

Weight of Depron sheet 12" x 12" x 0.25" = 0.8 ounces


That is to say, whatever weight your titanium displacer turns out to be (perhaps about 1 ounce), the same diameter displacer in 6mm Depron would weigh less than one sixth as much (perhaps 0.15 ounce)


So - can you do both and compare them? It would be a brilliant experiment as no-one has ever compared super-thin titanium displacers to the usual foam ones! I know which one looks better though (hint: titanium all the way!).

I thought I had posted this video here, but I guess not.


https://youtu.be/pU8mVkBZXv8


If you watch closely, looking at the foam displacer inside while turning the engine, it lifts up in the center, but the diameter of the engine is so large and the foam disk so thin and floppy, it doesn't actually lift up off the bottom around the perimeter.

Looking at Depron, (on some sites) it doesn't appear to be much, if any better. It is often sold in rolls. Apparently not rigid at all. Or maybe not the right stuff? It seems real Depron has been discontinued?

Some things advertised as "Depron alternative".

Ok, well I sent for some Depron, apparently, from someone on ebay. Hopefully the right stuff. If you could provide a source that would help

I have also been itching to try aerogel, but getting that anywhere seems impossible, other than blankets, that are not rigid at all, or very expensive tiny cubes.

I only have one engine, (other than smaller LTD type) so I can't exactly do a side by side comparison, but if I make some gaskets, rather than using glue or rubber cement, I can take the engine apart and maybe change the displacer, though I'm not entirely sure how it works or is put together. It is magnetic, so must have some metal at the center attached in some way.

May as well try some of this as well.

I don't think it is 100% fireproof but very light, rigid and strong as well as quite heat resistant I think.

https://youtu.be/ZUIr3AGan9I

Yes, I believe "Depron" as a brand name has disappeared now. But I still have sheets of the HobbyKing alternative and can post you some from the UK if you can't find any - it is very stiff, not floppy (you wouldn't want a floppy model airplane wing).

Carbon fibre sheet is a good idea, but being epoxy-based might go a bit soft at higher temperatures perhaps?

Aerogel would be prefect except hard to find and extremely fragile.

OASIS floral foam block is well worth seeking out because it has been used for displacers - it is readily available, easy to work, very stiff, very light and will resist higher temperatures (not sure how high, but reports I've seen suggest maybe 200 C before slight charring starts?

A very interesting engine...... looking forward to seeing the videos!

This could be nice, maybe. Kind of "period correct" though this engine is not really an antique.

These large mica sheets are available on Etsy. Maybe elsewhere. Several different colors.
It would certainly look nicer than carbon fiber. Not sure about the durability, mica is pretty strong. Generally fire proof, but this is composite. Natural mica sheets pressed together with bug juice (shellac), but apparently this combination can withstand temperatures exceeding 1500°F

Tom

Absolutely brilliant!!!!

You've hit the jackpot there, my friend. I'm kicking myself because I've been scratching my head for alternative materials and NEVER thought of mica.

I do know a lot about mica because I worked with it decades ago. It is a naturally occurring mineral found in igneous and metamorphic rocks. It has been mined in various places and used for hundreds of years to make little windows in cast iron stoves - as in your picture.

It used to be used in domestic heaters like toasters and irons as a flat former to wind heating wire around. It is a very fissile (it splits into thin layers easily) and this can be exploited to make thin sheets.

It is has extremely LOW thermal conductivity, it is light if you get it thin (split with a very thin sharp blade).

It is stiff (it is essentially a crystal which splits along one crystalline layer/plane).

Its only (small) downside is that it is a rock mineral (found in granites) and has rock-like density of around 2.7 to 3 grams per cc. So THIN is the way to go.


I wish I'd thought of it as it could be an ideal displacer (where you need a gap between the displacer and the cylinder walls).

Tom

I didn't know about the composite type. I have never heard of it before, and was only aware of the natural micas (there are several mineralogically distinct types of mica). It might be OK but cannot come close to the real material at high temperatures because the resin will eventually break down - exactly as you suspect. Also, the resin prevents the one thing that mica is famous for - you cannot expect to split composite mica into wafer thin sheets as easily as natural mica. Since weight is critical, thinner is better....

The most common type (because it naturally occurs in large crystals) is called Muscovite. You can still buy it - it isn't very cheap, but it is very good for what you need.

It is extremely heat resistant - way up to many hundreds of degrees C and it will not oxidise, burn, char, soften or crack (it is a rock-forming mineral).

There must be a number of sources of supply, here's one I found at random:-

https://www.agarscientific.com/afm-spm/ ... gIojvD_BwE

These are already very thin sheets and probably wouldn't need further splitting (though they tell you how to do it).

Thin mica sheet is traditionally cut with a pair of sharp scissors.

Tom,

This video gives a good "feel" for how mica handles:

https://www.youtube.com/watch?v=oXyPhBtMNqE

Alphax wrote: ↑Fri Feb 11, 2022 3:09 am
https://www.agarscientific.com/afm-spm/ ... gIojvD_BwE

Thanks

The 150 mm X 150mm should be just the right size. though would cost more than I paid for the engine

I finally had some time to take the engine apart

https://youtu.be/bGOXufXfgUo

The displacer cylinder is plastic. Not sure if it is acrylic or some other type of plastic, but definitely not glass.

The "bubbles" I thought were a "rough edge" in the glass or plastic were actually some sort of clear grease or Vaseline. The edge was actually quite smooth, though it looked a little misshapen.

The power piston compression seemed ok.

The main problem, I think, was the thin floppy foam displacer. Perhaps it had more rigidity at one time.

The little magnet embedded in the foam came loose.

I'll have to find a bottle the right size to cut a ring out of for a glass cylinder.

The holes in the wood base were drilled too deep, necessitating all the extra washers. It is almost drilled all the way through. Not much wood left for support.

I can't imagine that Vasoline maintained a seal for long with any expansion/contraction. I'm not really familiar with it as a sealant, whatever it is.

Nothing that can't be repaired and should be BETTER than new.

Thanks for all the information on mica. I kind of like the amber color though. I didn't know natural mica could be cut in such large sheets.

The composite stuff might work. Something I read about it said the bug juice, when used as a binder with mica pressed together under heat and pressure becomes very strong and heat resistant, but of course, pure mica would be better.

Anyway, I love the artistic design of the engine and the metalwork. The plastic and foam though, seems inappropriate for an engine that is apparently intended to run on even a small flame.

Upon closer examination, it does look like the plastic ring (pictured in the forefront), became too hot, softened and got squished. The entire ring shows deformation on what was probably the lower edge. That would explain why the engine had no compression as well as why the bolts were loose. The bolts we're probably all tight, but when the plastic softened, that was that.

The good news is I found several candidates for replacement parts; these two glass canisters as well as a large gallon jar.

The canister with the lid is made of heavier glass. The glass container the engine is sitting on is very thin glass. The gallon jar is probably about half way between the two. Any one of the three should work if I can manage to cut out a ring cleanly without cracking the glass.

I will probably need to make a bottle cutting jig for that operation.

Tom,

but when the plastic softened, that was that.

Looks like one of its previous owners wanted to find out if it would run faster if he put it on a hot stove!

Alphax wrote: ↑Sat Feb 19, 2022 2:37 am Tom,

but when the plastic softened, that was that.

Looks like one of its previous owners wanted to find out if it would run faster if he put it on a hot stove!

The way the engine was designed, the intention seems to have been for it to run on an alcohol or maybe kerosene burner, or a candle, or even a sterno, any one of which could easily get the brass plate hot enough to cause the plastic to soften.


The various, theoretically thin, lightweight, heat/fire proof/resistant materials I sent away for have been arriving.

Mica, Depron (supposedly), carbon fiber and titanium so far.

The Depron (not real Depron, probably) is nice and rigid, and super duper lightweight, but goes up like a match and smells like a burning rubber tire subject to direct flame

The resin binder burns off of the carbon fiber board, but the carbon fiber itself survives and remains strong and rigid, to a degree.

The shellac does burn off the composite mica sheets leaving clear sheets of mica which, separate and pretty much fall apart.

I'm sure any one of these might work, up to a point. The idea is just to be able to withstand indirect heat of a candle flame, inside the engine, while shifting hot air around, but just out of curiosity, I wanted to see what could survive the direct heat of a torch.

I think both the mica and carbon fiber could have the resins burned off and possibly continue working.

Of course the titanium came through the torch-er test relatively unscathed, though even that showed some slight warpage, but only slightly and that was heated up to white hot repeatedly with a direct propane torch.

The titanium seems rather heavy though.

I may still try making my own displacer from some kind of light weight refractory material.

Recently I've been looking into microwave kilns. I suspect they might be lightish weight, or maybe not.

Or ceramic fiber "paper" for use in microwave kilns.

Or maybe just regular kiln shelf board, that from this video, looks pretty light weight, (though quite fragile), which apparently could be sanded or milled down thinner.


https://youtu.be/7O9PrkMthcU

I'm also still itching to try thin sheets of magnesium alloy like used for making those very light weight nail guns.

Demonstration of a new flame resistant magnesium alloy combined with calcium:


https://youtu.be/DIRhveB1ppk


https://gondametal.jp/en/smarts/index/19/

Tom,

You have some nice materials there to play with. It will be very interesting to see which one gives you the most satisfactory performance.

Regarding temperature of operation, I know yours is a rather beautiful metal construction, but I have seen LTD engines with the bulk of the "framing" (for want of a better word) made in thin (3mm) laser cut MDF and some that are 3-D printed from ordinary PLA plastic. The MDF ones also had MDF displacers, though the 3-D printed ones had expanded polystyrene displacers. Though not beautiful - or durable compared with yours - they all work surprisingly well running off a little 'T' light candle without sustaining heat damage (the hot and cold plates were thin tin-can lids).

Sure, but I'm just testing stuff out while I have the opportunity, thinking beyond this little show piece of an engine.


I'm also looking for materials that can withstand extremely high temperatures, such as in a rocket stove, or coal burning stove.

My coal stove has at times gotten hot enough to soften the cast iron grate in the bottom, causing it to sag.


https://youtu.be/-xJXrBO7BLE

Besides that, I want this engine to run on anything from the heat of your hand to a blow torch.

The various materials, ("paper" and board) for use in kilns looks better and better to me.

This video does not show the actual firing stage, but the kiln paper and board can obviously survive heat high enough to melt glass.


https://youtu.be/QwITQ3FOcxY


Notice the firing temperatures at the end of the video. Up to 1420° F shown, but I'm sure it can go higher than that.

Tom,

Yes, those materials do look interesting. I used to have a microwave kiln made of the ultra light ceramic foam, but it was very fragile and when it began to disintegrate I disposed of it. It didn't respond well to even small impacts or compression (you can squish it between your fingers) but might be perfectly OK as a displacer if used with care.

One thing that you can do to toughen the outside of the light ceramic foam and dramatically extend its working life without adding weight is to carefully wet it/spray it with sodium silicate solution (look it up on ceramics sites). You need very little to dramatically increase the local strength of the foam - it is commonly used by furnace builders, kiln builders and potters to stiffen up ceramic blanket (ad hoc kiln liner).