As far as I know that is standard practice on longer motors, just
having the joint be in the center of a grain.
You can also glue the grains into the liner for some additional
sealing between the grain and the liner. You hopefully shouldn't see
much gas between your liner and the tube, so long as you have a decent
fit between the two. The gas in the core should expand your liner out
to fit against your case, as the case is the load bearing element. If
you have your seal between your grain and your liner good enough there
shouldn't be a path for gases to travel. Some grease on the inside of
the case might also discourage your hot gas flows a bit.
-Wyatt
On Thu, Aug 23, 2018 at 2:39 PM William Claybaugh <wclaybaugh2@xxxxxxxxx> wrote:
My 9” motor uses two pieces of phenolic tubing 34.75” in (nominal) length as
liner for 67.5” of case bonded propellant. This means that the joint between
the two pieces of liner is exactly at the center of the propellant grain.
Given that some hot gas will—intentionally—fill any voids between the liner
OD and the tube ID, it follows that such gas could ignite the back of the
propellant grain at the joint unless that joint is sealed.
Is there an experience in sealing such a joint against hot (or, at that
location, probably just warm) gas?
Thanks,
Bill