[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?

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..
----- 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.
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.


On 05/06/2014 03:59 AM,      (Redacted sender monsieurboo@xxxxxxx for DMARC) 
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.  
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 

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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