UndermineBriarEverglade
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Impact Sensitivity Apparatus?
I have built a hammer drop apparatus to test the sensitivity of ETN mixes, but am getting strange results. The apparatus consists of:
Tall vertical PVC pipe with cutout at the bottom for sample loading
1.3kg iron pipe sliding inside the PVC as a hammer
iron plug at the bottom of the PVC as an anvil
iron striker which sits above the plug
To test, I place 50mg of ETN on the "anvil", resting the striker on top of it, then draw back the hammer a certain distance. It drops down and crushes
the sample between the striker and anvil. The whole thing sits on a plank of wood on my wooden floor.
But over 10 tests, I have only had two detonations: at 150 and 180cm (the max height). If the apparatus is working correctly that'd be 23J, which is
way more than the reported 50% impact sensitivity of ETN (something like 5J). So something is going wrong. I greased the iron pipe to reduce friction.
Perhaps my striker and anvil are not flat or parallel enough, or the contact area is too large? Maybe I need a big steel plate for the anvil to sit
on? I'd appreciate any ideas, especially from people who have set up similar test equipment.
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Nemo_Tenetur
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This is my experience with my "ghetto style" IS measurement, posted lest year in exotic primaries - complex salts:
"Yesterday I´ve tried to set up an improvised "BAM-Fallhammerapparat" to measure the impact sensitivity of my sample, but after several trials I
gave it up. This is nothing you can do with "ghetto style" equipment and expect reliable results. An internet search revealed that it is really a
challenge to get an exact and reproducible value. Even the BAM federal agency in Germany (with state of the art equipment) emphasize the trouble and
problems in this area ("Herausforderung für die Qualitätssicherung"):
https://opus4.kobv.de/opus4-bam/frontdoor/index/index/docId/...
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UndermineBriarEverglade
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Thanks Nemo. I actually saw your post but couldn't figure out where to get access to that document. Do you have the PDF?
I tried sandwiching the sample between 120 grit sandpaper with no apparent increase in sensitivity. Also tried putting some bricks below the apparatus
with no improvement. If it is a problem with the loose-fitting striker not being exactly parallel to the anvil, or the faces not being flat enough, I
guess I could get access to a lathe and make a striker that slides into the anvil like the attached image.
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Nemo_Tenetur
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The complete document is restricted, available only within BAM federal agency network in Germany. Please read also the post from microtek and this
oblique pendulum test with sand paper, like a hybrid between impact and friction testing.
And please don´t forget the other dangers associated with electrostatic discharge, breaking of large crystals, insufficient purity and stability etc.
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Axt
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I suspect it's the anvil having too much give, it must be rock solid and very secure. Mine had a 1"x15" steel base plate and would reliably fire PETN
at a 45cm drop every time. I only used 5cm increments, trying to go get a more precise measurement would give you a headache. I wouldn't bother with
trying to calculate joules, just use it as a comparative measure specific to that apparatus.
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UndermineBriarEverglade
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I found that my "anvil" had deformed after several tests, so I removed it and put the sample directly on a small steel plate. I was able to detonate
ETN by whacking the striker with a sledgehammer instead of the pipe, so I figured the problem was insufficient weight. I filled the pipe with lead to
a weight of 3kg, but even from a height of 150cm I still can't get reliable detonation. Not sure what to do now.
Axt, can you describe the rest of your apparatus? I'd rather not buy a steel slab but if that's the only meaningful difference...
[Edited on 2024-11-2 by UndermineBriarEverglade]
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Axt
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Video attached, your description sounds the same. This rig was scrapped probably 10 years ago now, if you were to picture the ideal one in your head
it wouldn't look like this but was made with what was lying about. It was consistent though; I want to say it was a 3kg weight but cannot remember for
sure. Another possibility is your tube is too tight of a tolerance, if it's too tight or flexes too much it will be slowed by the vibration of its
release.
First vid is PETN firing at 40cm-45cm second is MEKP firing at 0-5cm. Interestingly AN-MEKP wouldn't fire at all up to 1m yet would fire when hit with
the lowest calibre rifle, showing that bullet impact is far more influenced by friction sensitivity than impact sensitivity. There's a surprisingly
weak correlation between impact and friction.
[Edited on 2-11-2024 by Axt]
Attachment: droptest_1408x1152.mp4 (6.7MB)
This file has been downloaded 74 times
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Axt
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Second
Attachment: mekp_2_compress.mp4 (4.8MB)
This file has been downloaded 57 times
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UndermineBriarEverglade
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Thanks Axt. Nice videos. The biggest difference is your apparatus isn't using a separate striker and it looks like you were testing larger samples.
I'll try removing mine. If that doesn't work I'll measure the speed of the pipe to make sure PVC flex isn't impeding it. Otherwise, time for a big
steel slab.
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Axt
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So you are placing the explosive of top of the anvil then a weight on top of that? If so that is the problem, think of the inertia that has and how
much it will take to get up to speed, it will have a dramatic effect on the sensitivity. If you are using a "firing pin" of sorts, you'll need to keep
it as light, rigid and as lower surface area as possible.
I was thinking how you'd make a dual purpose impact/friction tester, such as lever to convert the vertical to an oblique strike that can be folded up
out of the way like attached.
[Edited on 6-12-2024 by Axt]
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UndermineBriarEverglade
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I removed the "striker", cut out a circle of steel plate, and attached it to the front of the pipe. Surprisingly it didn't help. I then recorded a
slow-motion video of the impact. The "hammer" pipe is reaching the expected speed, so friction in the pipe isn't a problem. But the hammer bounces
several cm off the steel plate, and the whole setup - plate, base, and PVC pipe - jumps a smaller distance with it. I think I need a higher mass
anvil, equal or greater to that of the hammer.
That lever is a neat idea.
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markx
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Just use a free falling weight dropped by a release mechanism avoiding any guiding tubes or other restraints during the decent. And a very heavy
stable bottom anvil, this way you shall not encounter random deviations caused by friction and ensure consistent transfer of energy to the sample. A
basket around the sample holder shall catch the weight (a hammerhead, block of metal or any other weight of choice) so it does not bounce off the
apparatus and fall on your toes upon completion of the test  I've had quite
consistent results with such a device.....granted these results shall not be comparable 1:1 against a standardized measuring apparatus, but you will
be able to establish trendlines and compare relative sensitivities between samples.
Exact science is a figment of imagination.......
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Microtek
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But how do you ensure a square impact? If you were to use a hammerhead, it could easily spin just a tiny fraction of a degree, which would be enough
to make it impact the anvil but not the sample, at least fully.
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markx
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Quote: Originally posted by Microtek  | | But how do you ensure a square impact? If you were to use a hammerhead, it could easily spin just a tiny fraction of a degree, which would be enough
to make it impact the anvil but not the sample, at least fully. |
I use such a sample holder in the anvil. It protrudes from the bottom and makes for an easy target. Works very reliably...
 
Exact science is a figment of imagination.......
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