Rick...I recently learned about 'flex seal' and thought it would be ideal
for certain applications relating to rocketry as it cures to a nice hard
rubber, great for sealing shower stalls. I then tried it on a more
challenging application, sealing a hole in the wall of my AP synthesis
reactor. It turned to muck :-(
Anyway, I have not tried it in a rocket motor, and do not know how heat may
affect it.
Here is a suggestion. Epoxy or polyester resin (cheaper). Slit the casting
tube lengthwise using a saw with a 1/8" blade (or so), you want a gap.
Coating grain outside and casting tube inside with resin. Wrap casting tube
around grain and use band clamps to compress it snug. The remaining slit
gap can be sealed with silicone.
I've used a similar method with some of my ANCP motors that had compressed
powder grains.
R.
On Mon, Dec 19, 2022 at 3:27 PM Rick Maschek <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
Thanks for the input and suggestions, all have been discussed and I've
used several in the past but on 'smaller' 4 to 6" grains.
Our two piece 'safety nozzle' is built with a 6" hole in the convergent
piece. The 3.3" throat and divergent cone slides in from the outside and is
bolted on. If the pressure gets too great it is designed to blow off well
below casing burst strength, greatly reducing the pressure out the 6"
diameter 'hole' and saving the rocket while still thrusting vertically.
I've never yet tested the design but it seems like it would/should work.
I used up my supply of sorbitol on this 635 pounds of propellant motor and
was looking to buy another 1,000 or more pounds of sorbitol...STICKER SHOCK
at the current inflated prices for the next purchase. Mike Brinker has
offered some if we need to cast a new grain. The last time we bought some,
I think we bought 2,000 pounds and split it 3 ways. I found a place that's
even cheaper but when I called that price was for a 150,000 pound bulk
shipping container full from China...anyone want to go in for half? [image:
Emoji]
I am inclined to coat the outside of the propellant and the inside of the
new casting tube with epoxy, and slide the new casting tube over it while
insuring enough epoxy on top to get pulled in so no space is left empty as
the tube slides down. If some of the epoxy stays on top that will be fine
as we had thought about inhibiting the top surface of the bulkhead grain to
limit the heat to the bulkhead although we expect several inches of hot
liquid slag to form on the bulkhead. We also considered and still might
leave a 1/2" disk of plywood insulator on the bulkhead. As with our
previous motors, we expect EVERYTHING flammable inside the motor to get
consumed...casting tubes, O-rings, etc. Nothing was found inside the steel
case post-burn except the thick 4" layer of slag on the bulkheads.
Eric mentioned 'flex seal' yesterday. That would be the easiest and least
expensive to do but I've never tested it in a hot environment for a 15-20
second burn.
Thoughts?
On Monday, December 19, 2022 at 11:09:58 AM PST, Ben Brockert <
wikkit@xxxxxxxxx> wrote:
You mention “smallest core”: are you going for constant velocity through
all the grains, or a couple steps?
Weird to say, but congrats on not firing it. There are many projects
where’d they get go fever and say “ah well we’ll just fire it with one less
grain, it will be pretty close”.
On Sunday, December 18, 2022, Rick Maschek <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
Test firing was scrubbed, grain #5, the bulkhead grain with the smallest
core and the last one to be cast showed some casting tube debonding. Eric
slit the casting tube and we peeled it off. The Good news is that the
entire grain looked good, no cracks and only a couple of tiny voids (like
small bubbles). Surprisingly, considering it has the smallest core, this
was the hardest mandrel to remove with Eric having to pound on the aluminum
motor tube to remove it. The grain was very solid.
We are discussing how to repair it or if we make a new one.
On Sunday, December 18, 2022 at 10:43:55 AM PST, Daniel Kirk <
dk54321@xxxxxxxxx> wrote:
Can't wait to see the video!
On Sun, Dec 18, 2022 at 12:27 AM <dustin@xxxxxxxxxxxxxxx> wrote:
Your aren't going to static test it in that truck bed are you ?
Just kidding, I couldn't resist.
All the best,
Dustin
On 2022-12-16 09:23, Rick Maschek wrote:
Tomorrow may be the make-or-break day for Sugar Shot.
We will static test our 12" (300mm) five grain S-26,500 KNSB motor
with a total impulse of 355,000 Nsec
Finished 9' (2.7m) long motor case being transported to FAR
Rick
--
NULL
