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roXefeller
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Those capacitor designed detonators surely must have sensitive first fires. Which I find somewhat counterproductive to improve the safety of a device
by increasing the sensitivity of its components (bridge wires and first fires). It's like using nitroglycerin to improve the safety. WTF?
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Laboratory of Liptakov
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Location: Technion Haifa
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25% of failure ? It seems as a wrong joke. I am trying tomorrow do some pictures of my system, which works in basically without fail.
Development of primarily - secondary substances CHP (2015) Lithex (2022) Brightelite (2023) Nitrocelite and KC primer (2024)
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Bert
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Mood: " I think we are all going to die. I think that love is an illusion. We are flawed, my darling".
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Quote: Originally posted by aga  | | So, basically the go-to ignition system became no good and you need a new ignition system ? |
Not "No good" so much as our primary supplier (from who we maintain a half year + inventory of their products pretty much at all times) became
annoyingly and noticeably somewhat unreliable when used in a way I have done regularly for 20+ years.
We really don't like to take any explosives home at the end of the night.
What I feel a need for is our supplier to step up and try to improve feliability of their product, preferably in a way that doesn't increase my crews
risk of experiencing an accidental ignition. If our stuff goes off while attaching electric matches or in shipping, handling and loading into the
guns after, there will be injuries at the very least.
I have never had a crew person need medical treatment for burn or explosion related injuries. I'd like to keep it that way, the usual working guys
background count of twisting ankles, tripping over stuff in the dark, sunburns, blisters, insect stings, mishandling boxcutters, hitting fingers and
toes with hammers, etc. are bad enough.
This crew was attaching igniters to fireworks when they had an ignition. 3 out of 5 died.
http://www.wral.com/news/local/video/5503886/
[Edited on 11-3-2018 by Bert]
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sodium_stearate
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| Quote: Originally posted by Bert | | Quote: Originally posted by aga | | So, basically the go-to ignition system became no good and you need a new ignition system ? |
Not "No good" so much as our primary supplier (from who we maintain a half year + inventory of their products pretty much at all times) became
annoyingly and noticeably somewhat unreliable when used in a way I have done regularly for 20+ years.
We really don't like to take any explosives home at the end of the night.
What I feel a need for is our supplier to step up and try to improve feliability of their product, preferably in a way that doesn't increase my crews
risk of experiencing an accidental ignition. If our stuff goes off while attaching electric matches or in shipping, handling and loading into the
guns after, there will be injuries at the very least.
I have never had a crew person need medical treatment for burn or explosion related injuries. I'd like to keep it that way, the usual working guys
background count of twisting ankles, tripping over stuff in the dark, sunburns, blisters, insect stings, mishandling boxcutters, hitting fingers and
toes with hammers, etc. are bad enough.
This crew was attaching igniters to fireworks when they had an ignition. 3 out of 5 died.
http://www.wral.com/news/local/video/5503886/
[Edited on 11-3-2018 by Bert] |
Your job managing this is a very heavy responsibility.
Have you talked with other suppliers of these devices?
I ask because if your main supplier is starting to produce
an inferior product, then an alternate supplier would seem
like a viable thing to at least investigate so that you'll have
somewhat of a "plan B" when there is a need for it.
"Opportunity is missed by most people
because it is dressed in overalls and it
looks like work" T.A. Edison
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roXefeller
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So here is my thermal analysis of Bert's chart of no-fire/all-fire/arc regions.
I fit a power law regression to the lower curve of the all fire region. Not knowing the dimensions of the bridge wire I estimated the radius at 0.028
cm and a length of 0.2 cm. For a room temperature resistivity of 1.3E-4 ohm-cm this comes to one ohm. That small gage might be the reason for such
variations. I took density at 8.4g/cc, specific heat at 0.45 J/gK, conductivity at 0.113 W/cmK. This gives diffusivity at 298.9 cm2/s. The forcing
function F is constant at 2×I^2×L^2×r/(pi^3×cp×rho×A^2).
The solution to temperature at a point 0 <x <0.2 after a pulse duration of tp of I current, amps, is found by the following summation for
n=1,2,3...:
T (x,tp)=20+F•Sum {sin (n•pi•x)•[1-exp (-alpha•tp•(n•pi/L)^2)]•(1-cos (n•pi))}
Correct me if I'm wrong, but I see most of that lower curve heating up around 350C. Around 0.04s the isothermal assumption begins to fail (deviate
from assuming no conduction) and more current is necessary to maintain the temperature which is likely the reason for the elbow in the curve. Maybe
someone can plot it for me, I did all my work on an offline computer. I'll update it with the no fire curve when I get a chance.
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roXefeller
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So for the same geometry and thermal model it appears to stay below 200C in the no fire region. I used a power law of A=0.0455*t^-0.5205.
I was giving some further thought to the heat transfer from the wire to the pyrogen. The conduction equations are straightforward but I think they
are pointless. The pyrogen contact is discontinuous. The diffusivity is incredibly different. But at the same time I think there is value to
knowing the relationship. Given the high difference of temperature I think thermal radiation might be the dominant mechanism.
[Edited on 17-3-2018 by roXefeller]
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