I forgot to mention one important thing regarding obtaining good grain
density. After loading the casting tube with propellant, I immediately tap
it down against a hard surface (such as floor) repeatedly, perhaps a dozen
times. If there is any trapped air, it will be seen to rise to the surface
in the form of bubbles. Only then would I insert the coring rod and cap (if
using compression). Doing this is important whether or not compression is
used.
Richard
On Mon, Nov 23, 2020 at 10:22 PM Bdale Garbee <bdale@xxxxxxx> wrote:
"" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "tadserralt" for
DMARC) writes:
Richard just mentioned the possibility of increase burn rate due to
the modified formula.
Changing the oxidizer grain size definitely changes the burn rate.
I still think a void or crack or disbonding did it because the K-class
24 inch static test went very well
I agree that your most likely cause of CATO was a void. However, don't
ignore the fact that a faster burn rate means a higher operating
pressure for a given KN. Students I mentor seem to forget this
sometimes!
Until/unless you actually characterize the burn rate over pressure of a
"new" propellant after making changes in either the chemical composition
or processing steps (like grinding the oxidizer), assumptions tend to
lead to CATOs...
Bdale
