[SS-Propellant] Propellant "settling"

[dormans]

I cast a slug of KN/SB that was four inches long and 5/8th of an inch
diameter.   The casting tube was a piece of PVC pipe which I felt would hold
in the heat of the cast propellant and allowed the propellant to cool
slowly.  After it had fully cured, I marked the top and bottom of the slug
and then cut a one inch section from both the top and bottom.  These
sections were faced on the lathe and wrapped with a layer of tape to act as
an inhibitor.  The slugs were ignited at the top with a propane torch and
the burns video taped.  The burn rates were essentially identical, so it
seems that "settling" is not an issue.  The burn rate was .245 cm/sec, same
as I got for the BEM grains.

Randy

 From: Rich Nakka [mailto:richnakka at rogers.com] 
Sent: Tuesday, November 15, 2005 4:58 PM
To: dormans
Subject: Re: [SS-Propellant] Launch of the Propellant Development phase
ofSS2S 

Randy,
Would it be feasible to test your theory with some of the grains already
cast for the BEM? Scrape off some of the top & see how it burns? If this
simple test suggests that "settling" may occur , it  might also be
worthwhile for someone in the PDT to cast a test grain ...what do you think?

Richard

dormans wrote:
 

Richard's, Paul Kelly's and NEAR's  motors that are cited as exhibiting the
triangular thrust curve  when using Sorbitol all used bates grains that were
presumably prepared in the same way.  A casting tube filled from the top
with molten propellant and allowed to cool.  Is it possible that the KN,
being heavier, is settling a bit from the top and leaving a thin layer of
fuel rich propellant at the top?  So that it's not the space between the
grains causing the ignition delay, but that half of the grain ends have this
layer of fuel rich propellant that is delaying ignition.  The use of an
ignition primer or pyrogen ignition would not necessarily help if this is
the case.  Has this already been considered?  It's an easy theory to test,
just trim a thin layer off the tops of all the grains after curing or maybe
it would be easier to top off the grains during casting with a thin layer of
KN rich propellant or KN/SU as Tony has suggested. 

Randy

 

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