[SS2S-Main] Re: Material for Nozzle fabrication

  • From: "Cliff Bates" <cliff@xxxxxxxxxxxxxx>
  • To: <sugarshot@xxxxxxxxxxxxx>
  • Date: Tue, 6 May 2014 21:53:27 -0700

    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 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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