На AROCKET начали обсуждение точно такого же двигателя. Вот несколько писем. Кто-то читает AROCKET ? Ответите им ? Или пригласить их сюда?
Заметьте, как народу понравилась идея клееной камеры ;^))
We are considering ways of building a regeneratively cooled chamber. One option is to make it the “good old way” by means of pressed tubes that subsequently are brazed together. For this we believe we need to fabricate a mold milled in steel stock, and press the (oil filled) tubes in that. Might or might not work, but we have to start somewhere. I don’t recall reading about this on aRocket earlier. Suggestions are of course welcome.
Have anybody here any hints as to ways of transforming 3-D CAD models (such as from Autodesk Inventor) to G-codes for a NC milling machine?
I’ve been told that .DFX files can be transformed to G-codes by some utility, but which?
And how do I produce a .DFX file anyway?
Are IGES files relevant in this context?
If anybody has any knowledge, hints or pointers on this topic they can share, I’d welcome it.
Thanks – Henrik
DARK
Henrik-
NASA SE-019-008-2H-B "Feasibility study of A Pressure-Fed Engine For A Water Recoverable Space Shuttle Booster" (1972) describes a "constant area" method for forming chamber/nozzle contours without hydraulic forming of the tube.
Basically, a standard tube is (slightly) flattened to make the chamber bundle, allowed to grow to a circular cross-section in the converging section, then flattened in the opposite plane to "narrow" it for the throat; the reverse process allows it expand for the diverging section.
This method is mechanically simple and easy to produce. You will, however, need a brazing furnace for bonding the tube bundles once assembled--all the hand labor in
that (and the cost of maintaining large furnaces for low/no production) is the reason manufacturers now avoid this system whenever possible.
The "lithographic" process used for making platelet motors is by far the lowest cost and "coolest" (by reason of the far larger number of cooling passages possible) liquid engine technology currently available.
-Bill
Bill wrote:
“Basically, a standard tube is (slightly) flattened to make the chamber bundle, allowed to grow to a circular cross-section in the converging section, then flattened in the opposite plane to "narrow" it for the throat; the reverse process allows it expand for the diverging section.”
This is exactly what we had in mind. I just figured that to ensure a good shape (including correct angles between each tube element) pressing all tubes into the same mold would yield more reproducible results.
“This method is mechanically simple and easy to produce. You will, however, need a brazing furnace for bonding the tube bundles once assembled--all the hand labor in
that (and the cost of maintaining large furnaces for low/no production) is the reason manufacturers now avoid this system whenever possible.”
I like simple and easy, especially for hobby use J
I do recognize that one has to braze the whole unit in one go, to avoid local thermal stress that would change the chamber contour. However for the sizes that we plan to use (about 1’ in length) it should be doable using a home-made propane fired “oven”.
- Henrik
DARK
I have been thinking along the same lines, except my plan was to make a
mold of the tube, and then cast bismuth into the mold. Then
electroplate 100 to 200 microns of copper onto the bismuth. Then melt
the bismuth out in boiling water and start all over again until you have
the number of tubes you need. Then you stack your tubes, and furnace
braze or perhaps even diffusion bond the tubes together. Strengthening
bands can be added to the outside to help hold everything together.
Once I find another job, maybe I'll actually have enough money to try
it. Anyone have any job leads?
M. Spute wrote:
> I have been thinking along the same lines, except my plan was to make a
> mold of the tube, and then cast bismuth into the mold. Then
> electroplate 100 to 200 microns of copper onto the bismuth.
It is not that easy.
Electroformed tubes have no strenght against pressure and high temperatures
even, say 2
mm wall thickness ones: electroformed layers are brittle.
If you bend them they break. If you heat them the surface may start forming
bubble deformations from interstitial liquid traces.
(I tried that.)
> ...melt the bismuth out in boiling water and start all over again until
you have
> the number of tubes you need. Then you stack your tubes, and furnace
> braze or perhaps even diffusion bond the tubes together. Strengthening
> bands can be added to the outside to help hold everything together.
Also some the metal (you probably mean Wood's alloy since Bi has a melting
point of 271°C)
'll remain in the electroformed metal lattice and
drastically lower its
m.p.. Try to heat copperfoil contaminated
with solder: a hole quickly forms where the solder spot was.
Easiest thing to do according to a paper is to bundle, say, copper tubes on
a mandrel and electroform a, say Cu or Ni
coat several mm thick on them (I am thinking of a 2" dia. chamber). Next
embed stainless wire wrappings under stress and electroform again. Next use
a lathe...etc., etc.
(that I never tried; I fear it may take years to have a good product, even
in specialist labs with the know-how)
It remains a very complex operation, espescially connecting the manifold
passages.
JD
From: "John H. Dom" <john.dom@pandora.be>
Subject: [AR] electroformed motors... was Conversion of CAD model to G-codes
>
> It is not that easy.
> Electroformed tubes have no strenght against pressure and high
temperatures
> even, say 2 mm wall thickness ones: electroformed layers are brittle.
> If you bend them they break. If you heat them the surface may start
forming
> bubble deformations from interstitial liquid traces.
> (I tried that.)
>
Electroforming may be difficult for reasons given--though nickel
electroformed engines have been made.
But how about a copper tube bundle engine without brazing? If tubes are
formed (see
http://www.orionpropulsion.com for info about Tim Pickens' 12 K
engines, forming jig), then assembled around a form and overwouned with
phenolic/glass or graphite, the result could be ok. So long as hot
combustion gas cannot get out through the overwinding, the engine should be
ok. The phenolic wetting the outside and spaces between tubes will probably
not decompose at the bulk temperature of the copper tubes.
Charles Pooley
From: "ckpooley" <ckpooley@sbcglobal.net>
> But how about a copper tube bundle engine without brazing? If tubes are
> formed (see http://www.orionpropulsion.com for info about Tim Pickens' 12 K
> engines, forming jig), then assembled around a form and overwouned with
> phenolic/glass or graphite, the result could be ok.
Looks very OK. Maybe the carbon fibre motors of Beal were constructed in
that manner.
Note: I was never able to find out how the cooling liquid "returns" from
bottom to top unless they are ending up in
a common collector annular tube... which I never spotted anywhere.
JD
> From: "ckpooley" <ckpooley@sbcglobal.net>
>
> But how about a copper tube bundle engine without
> brazing? If tubes are
> formed (see http://www.orionpropulsion.com for info about
> Tim Pickens' 12 K
> engines, forming jig), then assembled around a
> form and overwouned with
> phenolic/glass or graphite, the result could be
> ok.
That's a pretty clever idea! I would think Aluminum
tubing could be used instead.
"John H. Dom" <john.dom@pandora.be> wrote:
> Looks very OK. Maybe the carbon fibre motors of Beal
> were constructed in that manner.
> Note: I was never able to find out how the cooling
> liquid "returns" from
> bottom to top unless they are ending up in
> a common collector annular tube... which I never
> spotted anywhere.
Everything I ever heard about Beal's motors, they were
just larger versions of the Scorpius motors,
silica/phenolic/ceramic cloth overwrapped with a
carbon/epoxy jacket. Chamber cooling was partly
ablative and partly film cooling.
>Note: I was never able to find out how the cooling liquid "returns"
from
>bottom to top unless they are ending up in
>a common collector annular tube... which I never spotted anywhere.
You can send coolant down one tube, and have it return in another;
essentially just one tube making a roundtrip to the bottom.
- Henrik
Charles wrote:
>But how about a copper tube bundle engine without brazing? If tubes
are
>formed (see http://www.orionpropulsion.com for info about Tim Pickens' 12 K
>engines, forming jig), then assembled around a form and overwouned with
>phenolic/glass or graphite, the result could be ok. So long as hot
>combustion gas cannot get out through the overwinding, the engine
should be
>ok. The phenolic wetting the outside and spaces between tubes will
>probably not decompose at the bulk temperature of the copper tubes.
What a wonderful idea... I like it!
Wonder if regular styrene/fiberglass would be able to withstand the heat
that inevitably slips through the passages between the tubes? Still, it
should be a nearly static pressure (no flow) so the heating effect
should be small.
Essentialy we are now talking about "gluing" the engine together. What a
concept
- Henrik