Marsh
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Detonator design
I would like to start this thread in hopes of shedding light on a topic which doesn't seem to be discussed too much specifically...detonator design.
It seems that while we may try to perfect a composition sensitivity-wise for proper detonation, I don't often hear about specifics of the actual det
design to be used. (And you can consider me speaking from my inexperience, but I think it is a quite reasonable topic of discussion).
Now what can obviously be gathered from commercial det design, is that they typically take the form of longer length/diameter ratios; slim designs.
Should all detonators be designed like this? Would a larger diameter be desireable in a det design at any time?
One of the things which I have been questioning lately is the production of the shock wave to initiate the material. In this scenario, I often ask
myself if it might be suitable to replace a high Vod primary charge with more quantity of a lower Vod charge in the det. This I haven't exactly
gathered a conclusion on just yet.
Another aspect is detonator material. Is the compression strength of the det case a property of importance?
For instance, I often chop clear 3/8"od acrylic tubing down for use as the det casing. I also use hot glue to cap the ends. My concern, is that the
soft glue on the end is acting as a shock buffer, therefore making the det design less efficient. This could also be considered for the acrylic case,
possibly being a shock buffer (although thin).
Is my assumption possibly true, or do the waves propagate through the det material with ease, relatively unaffected by material choice?
With these questions, I have considered using thin aluminum tubing for dets. Although, I have not decided what exactly to use for the end (if glue is
improper).
This brings up yet another question of concern for me. Could the aluminum tubing possibly hinder the detonation as well, if it indeed holds too much
pressure, thus delaying (in more proper terms, weakening) the initial det shock generated just a bit?
I have thought about the dynamics at play, and it would seem metal tubing would confine and possibly direct more of the shock out the ends of the det,
and emitting less shock from the outward cylindrical area. Should the det be designed to focus its energy to a specific point on the secondary, and
then allow the secondary explosive's shock to propagate the wave through the complete medium? Or should the design goal simply be to emit as much
shockwave as possible in all outward directions from the det? If a point of energy focus could be desired on the secondary charge, it would seem that
a shaped-charge style of detonator could initiate some of the less sensitive explosives requiring booster charges without one. Again, bare with me if
this sounds obsurd, just a thought.
The last of questions then arises from actual placement of the det. It would seem the shock should start from an outermost point, thus propagating
evenly down the explosive path. This would seem it should be inserted minimally, but enough to make intimate contact with the explosive. If inserted
all the way and the det is long, it would seem the initial expansion of the first primary (lesser Vod) would begin expansion of the contacting
explosive as it enters, but not initiating the detonation just yet. Before the secondary or booster is then reached, it would seem some of the
explosive would already be on its way outward and no longer in intimate contact with the final, massive shock. Or in otherwords, the contacting
material towards the powerful end of the det will properly detonate, while the other end of explosive is simply sprayed outward with lesser shock.
This is where I get my idea of minimal det insertion...I guess this may simply point out that the second primer in the det (like PETN) should be in
contact with the charge, and the initial primary end (like acetone peroxide) left non-exposed. Does this sound correct?
Hope this topic isn't too amateur for the forum, if it is I'm sorry, but I figured a few could benefit from some experienced input and discussion on
this topic. Thanks.
[Edited on 4-8-2006 by Marsh]
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ethan_c
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This is actually a very good question, one that I would like to have answered too. My interest in 'energetic materials' comes secondary to my interest
in plain ol' inorganic chemistry and element collecting. Topics like these are necessary, yet almost never discussed among more experienced amateurs,
oxymoron notwithstanding.
For example: easiest, generally most effective detonator one can manufacture at home? Particular substance, construction, materials, specific
safety…? I would love to hear any two cents' any old hands would care to put in.
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Nerro
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My guess would be on a sensitive substance such as Ag2C2 as the primary detonator, only a small globule on the end of the fuse. That would be embedded
in a slightly larger spherical shell of a less sensitive substance such as PETN or MHN. The whole detonator would be encased in something like paper.
It would keep the whole thing in place but not impede the shockwave in any way. This would be placed in the center of the explosive charge. If you
were to place the detonator on top of the charge a metal tube might be a better idea because then you can somewhat direct the shockwave into the
explosive but it wouldn't be as perfect because it would project a conically shaped shockwave into the charge rather than a uniformly distributed
spherical shockwave.
I think the shockwave must be uniform and from the center of the charge to ensure all of it detonates rather than part of it detonating and the rest
of it being scattered before it can detonate. With charges like ANFO I think this may be a real concern because I have heard complaints about such
charges only detonating partially again and again.
----------------------------------
I must say this is a lot of practical discussion so the mods might not really like this.
[Edited on Fri/Aug/2006 by Nerro]
#261501 +(11351)- [X]
the \"bishop\" came to our church today
he was a fucken impostor
never once moved diagonally
courtesy of bash
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quicksilver
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I have seen a concept that I would like to comment on; that of a "Flat" detonator. This was from a Canadian patent application wherein the detonator
was electric in design, a wide very thin bridgewire was placed in contact w/ a flash composition, then a primary of Pb azide and that seperated by a
thin sheets of plastic from PETN of .8gr. The device was the size of a tennis ball (approx 2") circular and wafer thin. The final product was sealed
with thin layers of plastic between materials. The presentation also digressed into the whole "plastic" detonator" issue too. The purpose was to
spread the detonation over a wider area of course. The illustrations showed a simplified production routine and detailed some issues re: density
levels and it's effects on blast waves in this "Flat" concept.
As a patent, I felt the guy was trying to hit too many ares at the same time. Production simplifaction, longevity, and blast wave alteration are
diverse enough so that he most likly wouldn't get royalties from it even if the application as it was written was accepted. but the idea of a "Flat"
det is unique when considering the use of the diamond shaped charge in cutting applications.
[Edited on 4-8-2006 by quicksilver]
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Marsh
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| Quote: | Originally posted by quicksilver
...The presentation also digressed into the whole "plastic" detonator" issue too. |
By this statement, it would seem that plastic is actually a less desirable material between contacting explosives, correct?
This is what I really question; the compression properties of the det material to influence on complete and efficient detonation of the secondary.
[Edited on 4-8-2006 by Marsh]
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Rosco Bodine
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This is a good topic that poses some interesting questions and I have done some experiments myself
seeking a better understanding of detonators , to discover what factors are in play and must be considered
in design of a detonator which will work efficiently and reliably . All other things being equal ( which is actually almost never the case )
miniaturization is the enemy of reliability and performance , so the design arrived at will inevitably be a compromise , particularly for practicality
for a commercial device or an otherwise standardized
design where dimensions are limited to a specified acceptable size . A blasting cap might have a fairly
wide range of size acceptability depending upon the
type of blasting explosives it would be expected to
be useful for detonating , and in fact different sizes by
numbers are available with that in mind . An entirely more specialized and restricted application would be the detonator design acceptable as part
of the firing train
in some sort of munition where the detonator must fit
within the allowable space available in a particular caliber of munition . So the design of the detonator is highly dependant upon exactly what is
intended to be detonated , and the allowable dimensions which the
detonator may occupy in the application , as well as
other physical specifications which must be met so that
the detonator functions as intended and most importantly functions properly at the time intended .
The minimum practical size for a detonator firing train is very dependant upon the choice of materials which will
be used in construction , and the smaller is the size requirement the more exotic must be the materials used
to reduce the dimensions . A detonator using more mundane materials in its construction will necessarily
have much larger dimensions which are its minimum functional size for a practical device .
Generally what I have observed is that the elements in a detonator firing train , as well as the output of the base charge itself , functions as a
sequence of * ribbon charges * which operate in succesion , each going through an accelleration through which the detonation
wave is increasing in velocity until a desired output is reached for the portion remaining , which then does
the work of detonating the secondary charge . The internal segments of the detonator are simply tasked with creating a rapidly accelerating
detonation wave
which is delivered to the base charge and induces it's
detonation in high order fashion , so that the impulse
is then transferable to the main charge . A detonator
is very much a " kinetic energy amplifier " which stepwise
develops a sort of " chain reaction " decomposition through its tandem elements , very much following the analogy of building a fire where the spark
lights the kindling and then the kindling catches the wood and then
the wood sets the whole forest ablaze .
If you can visualize it that way then you see the variables
which apply , as the intensity of the initial spark , and the
rapidity and flammability of the kindling , the properties
of the wood .....and certainly the nature of the forest will
all have bearing in how the " fire " progresses through its stages .
In a practical detonator made from the range of known and possible materials useful for the purpose , not just restricted to the better materials
commonly used for the purpose , the better performing materials would be useful
down to a minimum of perhaps 5.5 mm column diameter and at the other end of the range for milder materials
a minimum of 9-10 mm or even as much as 12.5 mm might
be necessary to guarantee absolute reliability in an unreenforced detonator . Whether the detonator is
reenforced or not also has great bearing and a reenforced cap which means strong confinement for the initiator , can halve the critical diameter
requirement as compared to an unreenforced detonator . So it depends on which design it is and the materials that are used in the construction , and
what is the intended main charge to be detonated , what will be a good practical design .
How these factors come together for a particular device
is therefore highly dependant on the application , hence there isn't really any such thing as a generic detonator ,
any more than there is any generic caliber of ammunition ,
but detonators like other " cartridges " come in all shapes and sizes and having different fillers for their
energetic components and encased in different materials different ways specific for the application .
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Sickman
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Marsh,
I found the following link very informative, and is illustrated with all the basic blasting cap designs.
Blasting Caps
Now in your post you use the term "detonator" which is a very general term to describe a host of devices designed to cause the detonation of a high
explosive booster or main charge.
In military usage there are fixed on several munitions "detonators" which initiate the firing train in the munition. Some are designed to detonate at
a certain altitude or upon impact ect.
However, I think what you have in mind is a basic blasting cap, either electric or non-electric(a visco fuse).
In my opinion, superior and cheap blasting caps are best made from aluminum tubing 6-10mm in diameter.
Because aluminum tubing is flexable it can easily be crimped.
The usual method would be to cut the tube to the calculated overall length that you want the blasting cap to be, then crimp one end. If making a
compound blasting cap with a base charge, first you would "press" a base charge of a secondary high explosive such as ETN, PETN, RDX, Picric Acid,
usually between 1-3 grams. Then on top of the base charge you would "press" a primary explosive such as lead azide, usually between .5-1.5 grams. Then
on top of this you would put a "loose" pyrotecnic charge such as lead picrate or black powder, usually between .1-.7 grams. An electric match or
waterproof fuse is inserted into the pyrotecnic ignition charge and then that end of the blasting cap is then carefully crimped around the fuse to
seal it.
Such a blasting cap would then be ready to go!
Great care and caution in combination with shielding and all possible protection should be worn when making such blasting caps in case of an
accidental detonation.
The cap is then placed completly into the high explosive to be detonated.
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vulture
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| Quote: |
Hope this topic isn't too amateur for the forum, if it is I'm sorry, but I figured a few could benefit from some experienced input and discussion on
this topic. Thanks. |
It's not amateuristic, but it is outside the scope of this forum. We like to keep our energetic materials section confined to the chemical side of
things. So no practical discussion.
Closed.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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