[SS2S-Main] Re: Material for Nozzle fabrication

  • From: "Hayk Azatyan" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "hayk_azatyan@xxxxxxxxx" for DMARC)
  • To: "sugarshot@xxxxxxxxxxxxx" <sugarshot@xxxxxxxxxxxxx>
  • Date: Tue, 6 May 2014 02:45:29 -0700 (PDT)

Thanks for the input Grant. Much appreciated. I just bought some 12l14. Where 
do you usually buy graphite from? 
On Monday, May 5, 2014 7:59 PM, Grant Saviers <grants2@xxxxxxxxxxx> wrote:
There are many choices of steel, the most popular for hobby machining is 12L14. 
 This is the easiest to machine steel and you can find "drops" from automatic 
turning operations in all diameters cheap on ebay.  The mechanical specs of 
12L14 are superior to A36 or ungraded hot roll steel (HRS) you might find at 
your local steel supplier.  However, it is near impossible to weld 12L14 
because of the lead content.  If you visit the rem center or junkyard then 
there is no at home way to determine the alloy.  

I found a continuous cast iron called Dura-Bar which has desirable
    strength at high temperature, think steel mill rolls and sourced it
    from EMJ (Jorgensen).  In 2007,  Richard & I machined the SS2S
    planned 100K nozzle from graphite (Richard) and Dura-Bar (me),
    turning 110 lbs of raw stock into a 10 lb nozzle and 100# of chips. 
    It's never been fired and it and the unmachined adapter to the motor
    ID block of Dura-bar (12" od x 5" thick) is sitting in my shop. 
    Also, cast iron is easy for low power/speed machining as the cast
    iron makes nice chips, not dangerous long swarf.  We have the
    graphite throat insert taper fit to the iron holding section (shell)
    and expansion side nozzle.  It is an excellent design IMO for a 10
    to 12" caliber motor although Kn might need a bit of tweaking
    depending on the core strategy.  

Graphite is a poor material in tension, better in compression. It or
    some ablative material is required for APCP.    A Dura-Bar or 12L14
    throat might withstand a few KNO3 candy firings, although HRS
    nozzles I made in the 60's did show some erosion.  I've seen step
    retained graphite inserts fracture and blow out on big APCP motors. 
    This is not likely to happen with a tapered insert as the more force
    the more the compression and also the better the seal.  Think about
    the forces, eg 1000psi times the square inches of motor diameter.

I've attached the pdf of the shell that holds the insert and the
    cert on the Dura-Bar alloy I chose.  I think the design scales
    easily.  Richard did a FEM analysis on the design.  I couldn't find
    the graphite insert drawing.  One more tip - as you learn to machine
    thin shells they will sing, ring, and vibrate so consider means to
    dampen them and always bore the inside taper first with the boring
    bar (which will also vibrate).

Grant Saviers

On 5/5/2014 4:10 PM, Hayk Azatyan (Redacted sender hayk_azatyan@xxxxxxxxx for 
DMARC) 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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