To me, your methodology – if enough scrutiny and care is taken – is sound
enough. There should be enough stretch (I know phenolic isn’t exactly the most
flexible of materials) to accommodate that level of clearance over a large
diameter although I’ve never used a ¼”(ish) thick liner before so…
In smaller motors, this issue is problematic for designs that completely seal
the liner with o-rings or whatever sealing so that no chamber gas is ever
exposed to the outside of the liner. Designs that allow the gasses to pass to
the outside of the liner (where the sealing is done against the motor casing)
tend to not be so susceptible to liner cracking. Not sure how common or sound
that approach would be for larger motors.
Troy
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of William Claybaugh
Sent: Tuesday, 24 April 2018 1:52 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Solid rocket insulation, yet again
I had a nice visit w/ Kory Kline over the weekend. Whilst looking over my
two-stage hardware he noted that because extruded aluminum tubes are always out
of round, he and found that phenolic liners failed by cracking into the
inevitable gap upon ignition.
His solution to this issue was to spin cast a liner of htpb mixed w/ carbon
black and then cast a monolithic grain into that lined tube. This seems to me
clever; he suggested that it does work.
My own approach has been to straighten the tube until the bulkhead will pass
through it, end to end. This leaves a maximum of 0.010” of clearance on the
phenolic liner (which has the same OD as the bulkhead); that has not proven to
be a problem in a total of eight firings at 9” diameter.
Are there other solutions to the extruded tube out of roundness issue?
Bill