[SS2S-Main] Re: Material for Nozzle fabrication
- From: "" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "monsieurboo@xxxxxxx" for DMARC)
- To: sugarshot@xxxxxxxxxxxxx
- Date: Wed, 7 May 2014 07:15:19 -0400 (EDT)
Because I occasionally machine graphite and this is the first time I've seen
this particular concern raised, I did an online search for info. I'd
characterize it as showing broad consensus but not unanimity. Based on that,
I've formed my own conclusion but really think anyone who creates graphite dust
should review the literature yourself and assess your own operations
accordingly -- always keeping safety foremost.
That's a fascinating and clever use of graphite in mining. LOX, like other
highly concentrated oxidizers, will sensitize most organics so I can certainly
see a combination of tamped graphite saturated with LOX being effective. Here
we have three separate cases (the mining case, graphite dust dispersed in
workspace air, and graphite dust dispersed in the shopvac canister or bag).
The fuel density and A/F ratios are different for each case, as is the
likelihood of an ignition trigger. It's certainly interesting to juggle the
variables involved while pondering the importance of "safety first".
I rarely cross-post but this might be a good question to pose on arocket.
It's been pretty quiet over there for the past week and the response from that
bunch could be informative. Any objections?
Cheers,
Mark L.
-----Original Message-----
From: Cliff Bates <cliff@xxxxxxxxxxxxxx>
To: sugarshot <sugarshot@xxxxxxxxxxxxx>
Sent: Wed, May 7, 2014 12:54 am
Subject: [SS2S-Main] Re: Material for Nozzle fabrication
I might suggest here that carbon dust is "extremely" explosive if mixed
with the proper amount of air and ignited. In fact carbon dust was used back
in the 1920's in mining to replace dynamite. A cardboard tube of packed carbon
dust was soaked in liquid oxygen for 15 minutes, then stuck in the blasting
hole. If the charge failed to go off for some reason, after 30 minutes the O2
evaporated enough that the explosive aspects of the charge became inert, so it
could be drilled out. Unlike the dynamite filled holes that the "new guy" got
to dig out........... alone.
Machining graphite is extremely dirty if a vacuum cleaner is not used, as
someone earlier pointed out. THE THING TO WATCH is the arcing brushes on the
vacuum cleaner motor igniting the dust if the vacuum cleaner exhausts through
the motor housing, as most do. I'd strongly suggest that the vacuum cleaner
bag be double bagged to assure the dust is all caught inside the can. If not,
a dust explosion could very likely occur from the arcing motor brushes as the
air/carbon mixture flows by, and it will not be a nice thing. Years ago I
accidentally sucked some coal gas fumes into my 5 gallon shop vac while
cleaning up after some blacksmithing. The vacuum exploded, splitting the can
wide open and throwing the lid with a 1 horse motor still attached, about 30
feet in the air. Graphite/carbon dust is much more energetic than coal gas
fumes, and why air powered drills are used in coal mining.
If you doubt this, take a large coffee can with a slap on lid. Drill a
hole in the side of it to fit a small 1/4" hose. Attach a small funnel to the
hose inside the coffee can and put a small amount, half a teaspoon, of flour in
the funnel set up vertically. Take a birthday candle and put it in the can.
Light the candle, then snap on the lid. Quickly blow into the hose to mist the
flour before the candle burns up all the O2 and goes out. Be sure to be back
about a meter or so from the can due to the exiting lid.
You can use this method to test various dust samples, including powdered
sugar, coal, graphite, flour, corn meal, fine wood dust, etc., etc. A larger
can with the same amount of "fuel" and candle will usually produce a more
energetic response than a large coffee can due to more air being available to
burn the fuel. However the idea here is not to level your shop, but just some
food for thought about something that is normally not considered..
Cliff
----- Original Message -----
From: Hans Olaf Toft
To: sugarshot@xxxxxxxxxxxxx
Sent: Tuesday, May 06, 2014 9:11 AM
Subject: [SS2S-Main] Re: Material for Nozzle fabrication
When using graphite for nozzles - keep in mind that it is a surprisingly good
heat conductor.
Hans
On 05/06/2014 02:39 PM, Steve Peterson wrote:
The Graphite Store (www.graphitestore.com). Right now, 2" rod, 48" long
(medium extruded) is selling for $66.50. That much steel would be a lot
more expensive. Unfortunately, I don't see any smaller diameters in the
medium-grained; they do have smaller diameters in the fine-grained but it's
more expensive--for instance 1" diameter by 24" long is $43.90. I would not
recommend trying to machine away a 2" diameter chunk if all you need is 1"
diameter--a vacuum helps control the dust, but it's still messy.
I used 12L14 for years before I switched to graphite and I still make steel
nozzles on occasion. I never saw any erosion with sugar propellant.
If you do go with graphite you can make a "form tool" for the convergent
and divergent sections which makes the turning go much quicker--just grind
down a spade bit, it doesn't have to be that sharp to get the job done.
--Steve
On 05/06/2014 03:59 AM, (Redacted sender monsieurboo@xxxxxxx for DMARC)
wrote:
Strangely enough, the mid-grade (medium-grained) graphite tends to do the
job better than the high-end, fine-grained material. Less erosion,
perhaps due to larger grains interlocking better and being ablated more
slowly. And of course, less expensive.
Graphite's definitely the way to go, but you don't want conductive, fine
dust getting into any electronics (such as a benchtop mini-lathe) so try
to capture the dust at its source.
Cheers,
Mark L.
-----Original Message-----
From: Hayk Azatyan <dmarc-noreply@xxxxxxxxxxxxx>
To: sugarshot <sugarshot@xxxxxxxxxxxxx>
Sent: Tue, May 6, 2014 5:53 am
Subject: [SS2S-Main] Re: Material for Nozzle fabrication
Thanks for your input Jeff. Where do you recommend I buy graphite from?
On Monday, May 5, 2014 4:58 PM, Jeff Moore <tnetcenter@xxxxxxxxx> wrote:
Graphite would probably be the most affordable of materials to use. We
had a machinist in our local group at one point and he made a titanium
nozzle as a proof of concept. That would more than likely be rather
pricey for this project ( his was for a 54mm motor).
Aluminum is a good material to practice on or do mockups with, but I
suspect that it's melting point is way too low to be used as the actual
nozzle. It might work as a carrier for a graphite or ceramic insert
though.
Jeff Moore
Bend, Oregon
On Mon, May 5, 2014 at 4:10 PM, Hayk Azatyan
<dmarc-noreply@xxxxxxxxxxxxx> wrote:
Hello all,
Would you all happen to know where I can get my hands on some scrap
circular steel bars for rocket nozzle fabrication?And if you have any
suggestions on the material I should use please let me know. I have
already started using the lathe, and currently I am machining a nozzle
out of aluminum. Although I will not be using this particular nozzle
for flight I figured I should practice making one out of some scrap
metal that I found(in this case aluminium). I know that you guys make
some of your nozzles out of graphite, but for now I am learning to
machine metal nozzles just for educational purposes.
Thank you guys!
-Hayk Azatyan
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