Wiley
Can it be done?
I cannot machine graphite due to the mess, but can graphite powder be pressed in a die to form a ready-made nozzle? This would presumably be a much less messy process than machining, since the powder could be more accurately "contained."
Senior Member
You can sinter graphite... that is to say one can.
new database user
How big is the nozzle you intend to press?
When I machine graphite the mess doesn't concern me, its not that hard to clean up and its a lubricant. I have seen others with a vacuum hose running while they are turning.
Wiley
The biggest nozzle would probably be 75mm.
My biggest concern with graphite dust is that it is conductive and can short out a lathe motor. This is a very significant issue because the lathe belongs to my dad.
Super Moderator
Graphite is easy to machine, and there is little cleanup if you use a shop vac to collect the dust as you make it.
While you can sinter graphite powder in a furnace, it's an industrial process that is done under vert high pressure and very high temperature. You can purchase Cotronics Resbond 931 graphite cement and make a polyethylene mold and cast it, but it is way easier and cheaper to machine graphite directly.
Bob
Wiley
As much as I'd like to machine it, such activities are verboten in our shop. I have heard that some people use steel for nozzles, particularly with rcandy propellants. Would a mild steel nozzle last for a couple firings with a "normal" APCP motor (~3-5 sec burn time)?
Senior Member
How about machining phenolic?Originally Posted by Wiley
Super Moderator
Buying parts may be the easiest way to begin.
You can buy any AT components from Rocket Motor Parts including phenolic for cheap.
For Kosen style cases, the preferred research motor casings, yoi can buy parts from Loki, Gorilla and AMW.
Bob
Wiley
Has anyone ever cast a refractory type concrete into the form of a nozzle and used it successfully?
Metal Head
I have cast refractory cement for use in a furnace, and the only concern that I have for a nozzle is that it might get a little chunky.... depending on the type you use.
Raw toast is an excellent alternative to bread.
Educated Redneck
For what it is worth.
The Shuttle SRB nozzles were carbon fiber wound phenolic resin
impregnated composite. After curing the phenolic resin the whole
assembly was baked in a furnace under nitrogen flow to graphitize
the phenolic resin without oxidation.
The reason I know this is the company I worked for back in the early
90's manufactured the resin and the best man at my wedding was the
chemist for the resin group.
Ron Lemke
When The People fear their government there is tyranny.
When The Government fears The People there is Liberty.
Thomas Jefferson
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Total Ns flown last year: 270.6
(I gotta fix that problem...)
Total Ns flown this year: 67.0
Wiley
Some castable refractory concretes are smooth as peanut butter. A little chunkiness shouldn't be that big of a deal, since I've seen some really coarse graphite nozzles. How do you think the strength of such a compound would compare with graphite? Graphite is a rather fragile substance, and it would seem to me that a high quality refractory concrete would be quite similar, strength-wise.
Super Moderator
Wiley
You can't use concrete for an APCP nozzle, it's too hot and the concrete is likely to shatter.
For cooler BP motors they use a clay nozzle, but that's not likely to survive APCP because of the temperature.
If castings refractory ceramic nozzles was a preferred method for hobby rocket motors someone would be doing it. No one is so it isn't practical and inexpensive. http://www.mcmaster.com/#ceramic-cas...pounds/=gcmlgy lists Cotronics ceramic casting compounds you can pruchase from McMaster-Carr. The zirconium oxide would be marfginal and is very expensive.
Again you can make nozzles out of Garolite Phenolic composites rods. http://www.mcmaster.com/#garolite/=gcmo2j LE,CE, and XX appropriate. They are single use because it will be erode just like AT phenolic nozzles from Rocket Motor Parts.
Bob
L2
Karl Amo, an advanced Pyro/ Rocket enthusiest posted the following intresting idea on Passfire:
Karl Amo
Posted 2/9/2012 8:12 AM (#183626 - in reply to #183607)
Subject: Re: Possible New Method for making Nozzels?
I have been developing an ammonium-perchlorate-composite-propellant [APCP] which burns hot; it turns fireclay nozzles and chokes to slag. The conventional solution to high-temperature propellant in rocketry is to use machined graphite and/or composites of of graphite powder, phenolic resin, and maybe even carbon cloth. When phenolic resin decomposes under high temperature, it turns into vitreous carbon - which helps to reduce the rate of erosion.
I have an idea for a composite nozzle, using off-the-shelf materials: graphite powder mixed with Weldwood Plastic Resin Glue, - a powder which is cured with water. Weldwood Plastic Resin Glue is a urea-formaldehyde material, which I believe turns to vitreous carbon when it decomposes. Once the-press-that-I-am-building is working, I will press some nozzles.
Super Moderator
The thermal decomposition/pyrolysis chemistry of carbon-carbon, graphite, carbon phenolic, silica pehnolic, and other resin systems is well known. A urea-formaldehyde mateial gassifies completely so it won't work.
breaks down completely to CO, CO2, H2, H2O, N2, CH4 on heating
Graphite is one of the fndamental forms of carbon. If you take a sheet of paper and cover the surface with interconnected hexagons, you would have the top layer of a sheet of oriented pyrolytic graphite. Take a ream of paper (500 sheets) with the same size hexagons, you have a piece of priented pyrolytic graphite. Each carbon atom in graphite is connected to 4 other atoms. In the case of the hexagonal form, in each plane at the apexes of the hexagons the carbon atom is attached to 3 adjecent in-plane atom, and weakly attatched to the layers above and below. In-plane heat flow is high due the the strong in-plane bonding, but out-of-plane heat transfer is much less due to the weak bonding, so in the out-of-plane direction it is a bit of an insulator.
Phenolic resin have a similar hexagon like carbon backbone, however some of the carbons have been replaced by oxygen, and some of the bonding capacity of the carbon is taken up by hydrogen. If you take a phenolic resin, and heat it in vacuum or under oxygen free conditions, you can remove the hydrogen, and the oxygen in a process called pyrolysis. and th carbon backbone rearranges to a graphite structure. This is why phenoliic resins work in a nozzle but urea-formaldehyde won't.
Almost all aerospace grade phenolic nozzles are highly processed in aparatus that no hobbyist has access to. You might be able to use a bis-phenol F epoxy resins and carbon fibers or graphite to make a molded nozzle but it would need high temperature dcuring. Epicure 862 or 863 are the easier of these to use, but there's no guarantee that it would work, and it would be single use.
For hobby use, it's hard to top graphite. In larger nozzle you can maching some of the phenolics I mentioned in a previous post nad use a carbon insert in the throat.
Web References:
Graphite
Chemistry of Epoxies / Epoxy Resin, Novolacs, and Polyurethanes
Epoxy
EPON™ Resin 862
Phenol formaldehyde resins (PF)
Urea-formaldehyde
In all honesty, there is nothing magical about nozzles. There are literally thousands of technical documents available as free downloads from the NASA and DOD on-line technical libraries that detail the materials, design and construction of nozzles. If you can't machine graphite or can't afford to have them made, you have no business messing aroud making rocket motor nozzles.
Bob
Wiley
Bob,
I have no problem machining graphite nozzles, or any type of nozzles for that matter. I have access to a lathe, and the only problem is convincing my dad that machining the stuff with a shop vac hose in close proximity to it is an acceptable operation.
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