Mike:
I have looked over Fike’s web site and I agree he seems the most
approachable.
My concern w/ engaging aerospace professionals is that this is at heart a
dirt simple device that appears to have been made remarkably expensive via
the common drive for technical excellence: I don’t require a pre-domed
bi-metallic gismo, I just need a simple disk that will clamp seal and break
when it is punctured.
Based on some conversations about what these things cost and one confirming
quote, I am pretty certain that for this application I need to make my own
because that will be far lower cost. Particularly given that a lifetime
supply is likely much less than twenty-five....
Bill
On Sun, Oct 25, 2020 at 4:25 PM Michael Kelly <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
My wife spent a lot of time on burst disks for a Northrop-Grumman kill
vehicle, and worked extensively with Fike - he was the only guy who could
make reliable burst disks. At the time, he literally worked in his garage,
and was a REALLY low cost supplier. Since then, he's moved into a
production facility, and has a website (
https://www.fike.com/solutions/pressure-protection/). His material was
nickel. That was a rude shock to my wife, who was looking at what would
happen to the kill vehicle propulsion system (which was already loaded with
propellant) over a delay of three months (until Raytheon could deliver a
seeker). The NTO had formed green crystals on the burst disk. From then
on, they gold-plated the burst disks.
Anyway, she says Fike was very approachable. Don't know much about him
since, but you might check out the website.
On October 24, 2020 at 5:10 PM, William Claybaugh <wclaybaugh2@xxxxxxxxx>
wrote:
Steven:
Thanks, that conforms with my thinking.
I’m testing the initiators this next week: two forms of nitrocellulose
(cotton and cord) to get a working unit with an initial cut on the amount
of gas generated, I am assuming the cord will prove easier as it can be
cut to a desired length vs. the guncotton which will need to be weighed.
I’m having disks made in three thicknesses in accord with the circular
flat plate model and will test each to burst in the valve assembly once
those are finished.
Final testing will then use the initiators to punch through the disk under
pressure...the trick there will be to find an amount of actuating gas that
does the job with one charge working but does not over pressurize with two
charges igniting. (I’m using dual redundant initiation In accord with
standard practice for pyro actuated devices.)
Bill
On Sat, Oct 24, 2020 at 8:36 AM Steven Berg <skyshredder9488@xxxxxxxxx>
wrote:
From my experience in using the flat plate model to design burst disks in
a few actuated systems, we used a circular flat plate to go into testing.
The overall thickness was typically all that needed to be varied. Adhesives
and clamping in the design were also the other first points of design
review.
On Fri, Oct 23, 2020, 2:27 PM William Claybaugh <wclaybaugh2@xxxxxxxxx>
wrote:
Having inhaled deeply of the arcana of burst disc sizing; I find that
the entirety of the available math is about sizing the plumbing, not about
design of the burst disc.
For my current actuated burst disc design I have a 1.5" diameter disk
that is clamped at 1.25" diameter. Operating conditions are air at
(probably something better than) -50 degree F (cold soak on the way to 200
Km) and at an original 125 psia. Using the standard flat plate model I get
this to be 0.050" thick disc of 6061-T6 providing a safety factor of 1.43.
If I am going to manufacture my own disk (an assumption worthy of
review), then is it correct to just assume a circular flat plate for
initial design, pending testing?
I will be testing prototype initiators next week; for now I am using an
e-match with a very small bit of nitrocellulose to generate the pressuring
gas. The nitrocellulose is in both "guncotton" and cord form. I expect
the former will be faster but the latter possibly easier to control since
cord length can be directly measured.
All testing will be at a local energetic materials facility...
Bill