Ral123
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low order detonations
I'm posting this topic bacause I'm little confused. I was reading about nitro and stragnely different people made tests-liquid, maximum density in
steel pipe 30-45mm and it says with blast cap No8 low velocity. With picric acid 8000+. With even more petn less then with picric acid. Supprisingly
there is low velocity for egdn too. In this forum I've red about etn/petn cast going low order too. I haven't had low order problems, but I'm
wondering about the pattern witch they folow. Does this happen only to the sensitive high power compositions? Most of us know that MeNO3 can be
initiated by it's own vapours, but what happens with the det. vel. then? There is some difference if it's by a spark ot by hot wire or may be exotic
platinum coated nail-ignition. Are only rdx/tnt and few more millitary explosives low order detonation proof? Will mixing the thing with inerts till
sensetivity is lowered make it low order detonation proof?
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dann2
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The exotic Platinum-coated-nail-ignition thing sounds interesting!
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Simbani
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MeNO3 detonates at nearly full velocity with the smallest available cap, it has the highest known sensitivity to initiation and will not go low order
if it get´s going by whatever activation. I had a low velocity det once in a lightly confined (straw) detonator with highly pressed ETN. It was
definately because back in the days I used SA DS(~150-250mg), therefore weak impulse. The one with 0,7g made a dent about 2-3x bigger and deeper than
the low-order 1,0g ETN (on the same plate with same casing). So i can be sure it was a low-order detonation.
" I was reading about nitro and stragnely different people made tests-liquid, maximum density in steel pipe 30-45mm and it says with blast cap No8 low
velocity. With picric acid 8000+. With even more petn less then with picric acid."
So there is it, different people made the tests. I bet that´s the reason that more PETN yields a lower VoD.. 
And it´s not only the high power compositions, look at AN/X (where X can be anything what can burn). A too weak shock gives a low-order det. only a
big booster kindles the true power. The reasons for low order tendency are numerous, that´s for sure.
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Ral123
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MeNO3 detonates more efficiently then NG with cap No1, according to one of the more popular books. With glass confinement both are much more prone to
maximum velocity. In my opinion mixing the nitric esters with secondarys like tetryl and hexogen will greatly reduce the low order tendency. Did you
know that 75% kizelghur/NG dynamite is said to detonate at maximum velocity(5000-6000) with No1 cap.
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AndersHoveland
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Tetrazene is very susceptible to low order detonation, if it is not adequately initiated. Its detonation velocity can vary between 1500 to more than
4000 m/s, depending on how it is initiated. For this reason, tetrazene was generally only suitable as a booster charge, not as a primary by itself. I
also have read of composition using tetrazine with xylitol-pentanitrate, which is supposedly much more reliably initiated, and potentially suitable as
a primary.
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Dany
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Almost all liquid explosive (e.g., NG, methyl nitrate, NG-EGDN) can undergo low velocity detonation (LVD). the explosive material is partially
consumed in the detonation wave. the remainder of the material is scattered around. The 1-dimensional Chapman-Jouguet detonation theory don't predict
this behavior of low order detonation, only high order detonation is proposed by this theory. Initiation of liquid explosive with a weak initiator can
generate LVD. Also, LVD is seen in detonating liquid explosive in cylinder near their critical diameter. LVD can have velocity on the order of 2 km/s.
It is important to say that both stable and unstable (pulsating non-steady detonation wave) LVD can occur. The confining material in the cylinder, is
an important factor that determine unstable or stable LVD. It has been shown [1] that when the sound speed in the confining material is lower (e.g.,
lead) than the sound speed in the explosive, an unstable LVD is generated . detonation in aluminium or steel almost always produce stable LVD. The
mechanism proposed for this observation is that precursor wave propagate in the confining material ahead of the detonation wave, creating cavities
resulting from the cavitation of liquid explosive due to expansion (remember that a fluid cannot support tension wave, liquid will cavitate under
tension wave) which play an important role (may be as a hotspot) in sustaining the delayed detonation wave. but as a general conclusion LVD is
produced when liquid explosive are initiated with weak iniator at nearly critical diameter.
Reference:
[1] detonation in liquid explosives-the low velocity regime, R.W.Watson, C.R. Summers, F.C. Gibson, and R.W. Van dolah, 4th
international symposium on detonation, page 117.
Dany.
[Edited on 28-8-2013 by Dany]
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AndersHoveland
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One strategy to make these compounds resistant to low order detonation is to mix in another explosive that is not vulnerable to undergoing a lower
order detonation.
[Edited on 28-8-2013 by AndersHoveland]
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dangerous amateur
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Do you know what these numbers mean or what equivalent amount of what stuff they represent?
| Quote: |
It was definately because back in the days I used SA DS(~150-250mg), therefore weak impulse |
I find that very much for ETN...
What do the experts say, how many DS would you put in your caps for best reliability?
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Dany
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numeration of blasting cap indicate it's strength. there are 8 strength ranging from No 1 (weakest) to No 8 (strongest). Indeed as the strength
increase so dose the quantity of priming charge. No 6 blasting cap contain 1 gr of 80/20 mercury fulminate/KClO3 while No 8 blasting cap contain 1.6
gr Hg(OCN)2 and 0.4 g KCLO3. we can notice that this quantity is not small, because these blasting cap are called single component cap. the primary
explosive can be reduced to few hundred of milligrams (e.g, 200 mg of lead azide) coupled with 0.5 g of secondary explosive (e.g., PETN). these are
called compound blasting cap and are much stronger than single component cap (because of the presence of secondary explosive acting as a base
charge).
ETN has been used in old compound detonator. for making such detonator see the attachement below. for more information on blasting cap see
Encyclopedia of Explosive and related items, Vol.2, page B-185.
Dany.
Attachment: detonator.pdf (79kB)
This file has been downloaded 551 times
[Edited on 28-8-2013 by Dany]
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Fantasma4500
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i know a 'No 8' cap would be approx 3g in total of 10:90 lead styphnate ETN
(fluffy, pressed or cast?)
we had a visit from an explosives expert but in my country im not sure how much you can take for word, he didnt mention total amount although, but i
have heard several places (nope, cant remember sources) that its about 3g in total
he showed where a blasting cap was set off in a metal can (steel?) and the sure pattern of the aluminium fragments could be seen, very interesting,
nearly artistic.. although something makes me wonder... wouldnt at least 2.5g PETN be enough to remove a such can? can had diameter of appox 15cm
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Ral123
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I guess you need a booster for almost every maximum density/high density material. TNT, TNP, RDX-PBX, OCTOL, Trtytol. The nitric esters don't need
that much. Few grams crystaline RDX and they are UP.
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Dany
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initiating high explosive charge is a complex topic and depend on many factors not only on the iniator. The sensitivity of an explosive material is a
chemical and physical problem. Every one knows that nitroglycerine is sensitive, but this feature is not of chemical nature only (e.g, presence of
weak -O-NO2 bond in nitric ester). in fact, one of the experiment done on nitroglycerine shows that removing microscopic bubble gas from
the liquid, decreases the sensitivity of the explosive. Of course, explosive at theoretical maximum density (TMD) are harder to initiate due to the
lack of active site that form hotspot after the passage of detonation/shock wave. In some cases, it is advisable to add solid material to increase
sensitivity. for example, pure nitromethane is very hard to initiate (even with an intermediate booster charge) but adding glass micro-balloon (GMB)
to the solution increase the sensitivity of liquid nitromethane. 3% Poly(methyl methacrylate) (PMMA) are added to prevent the GMB's from settling-out.
Some time nitromethane can be sensitized by chemical mean (e.g., adding amine or acids). The physical state of the material (fine or coarse) will
affect the sensitivity of explosive. The type of confining material, temperature...all affect the pressure threshold for the initiation of high
explosive.
Dany.
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Ral123
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I've heard that if you confine your stuff with maximum density, hard material like glass, the high velocity is easier to obtain. Do you know how
kizelghur makes NG to be set off reliably with weak initiators?
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Dany
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adding fine glass or fine sand will increase sensitivity/lower the critical pressure of initiation. compared to pure material, the addition of sand or
glass will serve to attain maximum velocity in shorter time or decreasing what we call run-up distance. suppose a stable detonation wave (constant
detonation velocity) is achieved after 10 microseconds of the entering of the shock wave into pure explosive, the time will be for example 1
microsecond for explosive mixed sand/glass material. Indeed the inert solid is added in small proportion because after a certain limit you loose
explosive energy because you are diluting you explosive charge with inert stuff. Remember that in order to increase sensitivity of explosive by mean
of inert solids, the latter should have a melting point above of that of the explosive material. if the melting point of the added inert solid is low,
it will melt after the passage of the shock wave. Melting will consume energy from shock wave and then the latter will fade to a point were chances of
initiation is almost impossible. However, high melting solids tend to concentrate the energy from shock wave around them, and hence rising the
temperature well above the remainder of the explosive charge. the chemical reaction start at this point (called hotspots) forming many waves. these
waves will coalesce forming a detonation wave. this is the heterogeneous mode of initiation in detonation theory. pure liquids and single crystals
explosive obeys the homogenous mode of initiation.
Dany.
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dangerous amateur
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I meant especially the No.1 Cap.
Concerning mercury fulminate - have you compared this to DS?
DS seems to be the perfect stuff if it wasn't so static sensitive.
That they are both weak does not bother me. I want the "safest" stuff. I don't care to spend 400mg or more to initiate ETN boosters.
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Ral123
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Quote: Originally posted by Dany  | adding fine glass or fine sand will increase sensitivity/lower the critical pressure of initiation. compared to pure material, the addition of sand or
glass will serve to attain maximum velocity in shorter time or decreasing what we call run-up distance. suppose a stable detonation wave (constant
detonation velocity) is achieved after 10 microseconds of the entering of the shock wave into pure explosive, the time will be for example 1
microsecond for explosive mixed sand/glass material. Indeed the inert solid is added in small proportion because after a certain limit you loose
explosive energy because you are diluting you explosive charge with inert stuff. Remember that in order to increase sensitivity of explosive by mean
of inert solids, the latter should have a melting point above of that of the explosive material. if the melting point of the added inert solid is low,
it will melt after the passage of the shock wave. Melting will consume energy from shock wave and then the latter will fade to a point were chances of
initiation is almost impossible. However, high melting solids tend to concentrate the energy from shock wave around them, and hence rising the
temperature well above the remainder of the explosive charge. the chemical reaction start at this point (called hotspots) forming many waves. these
waves will coalesce forming a detonation wave. this is the heterogeneous mode of initiation in detonation theory. pure liquids and single crystals
explosive obeys the homogenous mode of initiation.
Dany. |
Thanks, for your scientific answers.
Would you suggest lead confinement, when it's desired to have a reliable product, that would force great pressures at the opposite end of the
initiation?
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Dany
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Ral123,
i don't recommend lead, because it has low yield and tensile strength compared to steel. so the resistant of steel is better than that of lead.
Dany.
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Ral123
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I agree on that when it comes to deflagrations, for example FP confinement or NG at low diameters/speeds. But when it comes to HE's I didn't think the
tensile strength will matter, specially at 200+k.bars of liquid/cast nitro ester.
http://www.youtube.com/watch?v=6rRg7ksNaZs
Here the tough steel container became dust, that did nothing to the fragile objects, and that's Tetryl, it's not even ETN.
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Dany
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Ral123,
the idea of steel being totally pulverized or vaporized is not true. Detonation wave don't have the energy or the time to vaporize or
completely pulverize metals. if this was the case (vaporization and pulverizing) explosive will become useless in artillery shell because only
tiny fragment will be produced which have little penetration ability and looses energy in an exponential manner with distance to the target (P.S.
velocity of large fragment also decay in an exponential manner). A normal cylinder like the one in the video, will undergo a natural fragmentation
generating large, medium, small and very small fragment. the distribution of fragment size can be predicted based on Mott equation or other
relationships [1]. first the video on youtube is filmed in the dark (which is the worst situation for analyzing an explosive event).
The conclusion at the final of the video is wrong because if he didn't find fragment in the items (bottle, wood...) around the explosive charge after
detonation this doesn't mean that fragment are not produced. first the arrangement of the test is wrong, the item should completely surround the
explosive charge (like plywood panel) and the explosive charge should be in a vertical position so the fragment are sent radially. when you lie the
explosive charge on one side, the fragment tend to enter the earth and some will go upward. don't forget that there is a probability hit when a
fragment is intended to engage a target. I'm sure that if he repeat test in the right condition, he will find a distribution of fragment size.
[1] Tactical Missile Warheads (Progress in Astronautics and Aeronautics) J. Carleone.
i recommend you to read the book of reference [1]. this book is an important book on warhead and fragmentation phenomena. you can download the book
from here.
http://libgen.net/view.php?id=918393
photos of professional detonation test arena:
also, a nice video from oregon ballistic lab showing the explosion of car bomb loaded with ANFO. at slow speed and @12-13 second one can see how the
fragment surpass the shock wave in air, the shock wave looses energy faster than the fragments, so the fragment at certain point will be faster and
surpass the shock wave in air.
http://www.youtube.com/watch?v=UPSz62a-C44&feature=c4-ov...
Dany.
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[Edited on 10-9-2013 by Dany]
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Ral123
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I thought warheads are with metal cases so that the same volume will generate more mass, flying around, and secondary are the fragments. My impression
so far is that in larger diameter charge, no matter how powerful the material is, there will be significant fragments( http://www.youtube.com/watch?v=w0Xk-TgGcDE ). Also, thicker container, doesn't mean bigger fragments, till a certain point.
This test in a brittle arrowtube gave high velocity micro particles( http://www.youtube.com/watch?v=luj3NdyBisA ) I'm not sure if the brisanse was low, or fragments were genereted because the material was pressed
and micro hollow spots were created, preventing even pulverisation.
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