Sciencemadness Discussion Board

Detonator Casings

golfpro - 22-9-2013 at 18:02

So I am trying to have caps that are as reliable, safe, and storage stable as possible. I have the materials to make an industry grade blast cap (maybe not quiet), but I don't want the casing to just be drinking straw, and risk friction and other issues. Has anyone found a way to make a nice uniform Al tube/case w/ thin walls for caps?

[Edited on 23-9-2013 by golfpro]

Bot0nist - 22-9-2013 at 18:22

Aluminum arrow shafts are where its at. Brittle and consistent... Cut off sharpie marker backs too, or small HDPE test tubes if plastic is desired. Drinking straws are a terrible idea, in my opinion. Much too flexible and elastic. Accident waiting to happen.

Play safe.

confused - 22-9-2013 at 21:06

being an archer myself, the thought of cutting my arrow shafts makes me cringe, anyway arrow shafts are expensive, why not use the cylinder of cheap ballpoint pens?

Microtek - 23-9-2013 at 04:21

Buy a small lathe. Use it to bore an aluminum (or steel) rod to the desired dimensions. Then use it for producing rocket nozzles, or as a starting point for a great new hobby that complements HEs nicely. Once you get some PTFE rod, you can make your own lab-ware without the glass-blowing.

Bot0nist - 23-9-2013 at 04:54

Brittle metal is usually desired over plastics so that the cap doesnt "balloon" out at the moment of initiation and create a seperation from the secondary. Metal arrows are not that cheap, but much much better than plastic pen cases. A single arrow would make many small caps I bet.

[Edited on 23-9-2013 by Bot0nist]

bfesser - 23-9-2013 at 05:43

Can't you purchase short lengths/diameters of suitable aluminum, brass, steel, and stainless steel tubing from hobby supply shops (or hardware stores)?

[edit] Admittedly, it can be expensive, but so is burning/exploding all of your chemicals.

[Edited on 23.9.13 by bfesser]

Fantasma4500 - 23-9-2013 at 10:13

well i think bfesser of what ive seen the tubes are too thick, what would be desired would be like a permanent marker casing, in which ive heard being used.. perhaps some stores or some online buy a tonne
of what ive seen theyre usually aluminium
otherwise guys
go buy yourself some aluminium foil tape, the thick kind..
you can then wrap this tightly around a straw and cut it however you want to, it should be possible to put on more layers to furthermore harden the external casing..

golfpro - 23-9-2013 at 18:25

I'll look in the hobby store tomorrow for something like that, but right now I have good sized cases, but they are plastic, I'd like to get an industry identical, but IMO, straw makes for good reliable initiation, but doesn't protect the materials inside very well.

Mathias94 - 23-9-2013 at 22:48

I don't know what your primary of choice is, but remember that mercury fulminate and probably a lot of other primaries is uncompatible with aluminium.

Mathias94 - 23-9-2013 at 23:09

EDIT: Double post, a moderator may delete this :)

[Edited on 24-9-2013 by Mathias94]

Ral123 - 23-9-2013 at 23:20

Copper for fulminate, Al for azide or I messed this one up badly?

Pulverulescent - 24-9-2013 at 04:18

Quote: Originally posted by Mathias94  
I don't know what your primary of choice is, but remember that mercury fulminate and probably a lot of other primaries is uncompatible with aluminium.

HMTD, the most useful of the organic peroxides, should not be used with any metal other than aluminium . . .

golfpro - 24-9-2013 at 06:07

SADS works well with aluminum casing.

Gargamel - 24-9-2013 at 07:25

I wonder how SADS reacts to static discharge in such an aluminium cap. I only work with visco fuse.

I wonder if the fuse, that contains (somehow conductive???) charcoal but is isolated on the outside, like a coaxcable, can create a breach in the faraday cage?

Also it leads directly to the primary, so any incoming current would have to pass the primary...



These things seem so simple, but are so complicated in detail, I'm a bit worried if this can ever be handled by hobby guys like us. IMHO such a cap must be safe to be handled once closed.

I would assume that an aluminium cap is mechanically save as long as you don't drop a big stone on it. The only thing that remains is static, especially with SADS...

Endo - 24-9-2013 at 09:01

Befriend someone who works at a bow-shop. The typical process with a new arrow shaft is to trim them to length for the archer using them. The scrap typically goes into a drum for recycling.

CaliusOptimus - 24-9-2013 at 11:02

0.253" ID x 9/32" OD aluminum 3003 tubing is imo a perfect choice for caps. It is soft enough to form, but strong enough to handle around 5000psi during pressing. Lots of hobby shops and hardware stores have it in 1' lengths and mcmaster has it in 1' or 6'. It's cheap to boot.

Blasting cap from paper

dangerous amateur - 5-1-2014 at 04:27

Hi guys,

i just thought about using paper tubes for blasting caps.

I have some pyro related spolette tubes, they are 7mm on the inside and little more than 9,4mm on the outside. Wall thickness is about 1,2mm.

I figured that these will give at least some protection for a primary while handling the cap, and no dangerous shrapnel. On the other hand, there is a zone of rather low density (compared to Al) paper between the caps booster and the secondary.

I'm not sure if paper is good or bad concerning ESD. But I read suggestions about how to package semiconductors, and I remember somehow that "paper is not too bad, also it always accumulates some moisture"

How do you feel about using paper, looking at perfomance and safety?

greenlight - 3-11-2014 at 17:43

Al tubing for model plane construction from hobby shops is perfect for dets.
I successfully used soft drink can aluminum when i have run out of tube though as it is quite thin.
Cut the top and bottom off an empty soft drink can and cut a small rectangle from whats left. Roll it tight round a small pen or dowel and tape. Once forcefully rolled a couple times you can get a very small tube from it.
Then push a small paper tissue plug through with the dowel to act as an end cap and fill with primary, place a fuse with some more tissue around it and tape the top. Insert into explosive when ready.

Hawkguy - 3-11-2014 at 18:04

Try using tent poles, bought for spares. Most are dreadfully thick, but some might work...

roXefeller - 6-11-2014 at 19:31

I just found a pile of discarded arrows at my gun club archery range. They were bent or fletchings were damaged and then discarded. You can also find these things on ebay as auction lots of either functional arrows or whatnot. You can find them at a price of $1 per shaft. The trick is choosing an elegant method of closing the bottom. As a way of keeping this post scientific (here's looking at you Bert ;) )... +2 for brittle/high strength aluminum tubing. On the fracture toughness curve materials like this will absorb less energy during a charpy test demonstrating that less deformation energy is taken from the shock front... the material will deform elastically until the fracture point as opposed to a material that will transition past the elastic behavior into the plastic deformation zone and absorb energy inelastically. Though this shouldn't matter much if the quantity of primary is sufficient. And one last note, primaries don't really get characterized by critical diameter, but a composite cap with a boosting secondary should force you to compare this secondary critical diameter with the tube ID.

TGT - 10-11-2014 at 15:25

22 Magnum bullet casings I think would be perfect. You could heat them red hot and crash them in water or oil to make the metal more brittle, just a suggestion.

TGT

UnintentionalChaos - 10-11-2014 at 16:53

Quote: Originally posted by TGT  
22 Magnum bullet casings I think would be perfect. You could heat them red hot and crash them in water or oil to make the metal more brittle, just a suggestion.

TGT


What, brass? Copper alloys readily anneal even with rapid quenching.

roXefeller - 10-11-2014 at 19:29

According to this copper alloy hardening article, you are more likely going to find non-quenchable brasses in brass cartridges. The typical path for hardening material like that is cold working, where grains are shaped by continual material damage without heating, which would cause grain growth and softening. The earlier article also mentions other methods, precipitation hardening being very common where bits of metals precipitate out of solid solution.

packetforger - 12-11-2014 at 11:14

Avoid metal casings like the plague. Not only do they produce nasty metal shrapnel, but also, can react with certain primaries.

Back in the day when I used to experiment with such things, I often used paper casings dipped in the "liquid glass" sodium silicate solution to give them more rigidity. A couple windings of paper around a dowel rod, fold in the end, dip the tube in the "liquid glass", and let harden up. You end up with a nice cap with thin walls (which should transmit shock better), decent rigidity, and no scary metal parts.

The same liquid glass stuff can be used for all kinds of things, like reinforcing casings of salutes and such for a louder pop.

Microtek - 13-11-2014 at 00:56

Also, you get a detonator that is more prone to transportation mishaps because of the lower structural strength...

Hennig Brand - 13-11-2014 at 10:58

I agree with Microtek, also even small increases in case thickness significantly reduces the effective transfer of impulse from the explosive in the cap to the secondary to be initiated. Metal casings can have very high strength even when relatively thin.

Detonator Materials

DetaDude - 2-12-2014 at 16:39

When I had my consulting co. we used to make up "look alike bombs to imitate real letter bombs and other types of explosive package's" and when it came to producing the detonators we used hobby shop K&N aluminum tubes with a dowel inside to keep it from bending etc. We were training police and fire first responders
how to handle bomb threats et. al. The point here is that the finished product looked
like the real McCoy. and the tubes were soft enough to roll them on a hard surface
until we got the end to look like a factory made working detonator.

kecskesajt - 14-12-2014 at 03:50

Paper is better than any metal blasting caps.On another pyro-site I heard that somebody used iron blasting caps and after det. he heard iron pieces flying and whistling.Quite unsafe.

ecos - 14-12-2014 at 07:33

I use syringe.
syringe would be better than paper.

hissingnoise - 14-12-2014 at 12:34

Soft aluminium tubing (silvery confetti) from an old freezer; good for most primaries except mercury fulminate . . .

NeonPulse - 14-12-2014 at 15:38

Most hobby shops stock Al tubing in various diameters. Cheaply. Seal the end with a little epoxy putty, insert a straw or paint with nail polish for extra safety and your good to go. The only problem is if the base charge is pressed too hard you will deform the end.

Hennig Brand - 14-12-2014 at 19:23

I was doing that for a while; gluing a slice of hardwood dowel or using an epoxy plug in the end of a detonator casing. It does work, but it is not ideal. The bottom end of the detonator, opposite the ignition end, is where the velocity and pressure are at their greatest and therefore it is also where the cap has the greatest initiating ability. Separating the bottom of the explosive charge in the cap from the secondary to be initiated with a thick plug of glue or wood, or whatever, significantly reduces the transfer of the strongest impulse the cap has to offer for initiation. The sides of the cap are still effective, but a lot is lost by putting a thick layer of material at the end IMO.


[Edited on 15-12-2014 by Hennig Brand]

NeonPulse - 15-12-2014 at 04:06

I agree there. I guess perhaps drawing the end over a small steel bar with a tiny disk of metal to fit the hole may work well to stop the large plug being needed if you know what I mean. You would place the tube over the steel leaving a few mm over the top of the bar, put the disk in place and heat gently as not to melt the Al and draw the edge over the disk. Seems like a lot of fiddley bits but if you could get a system giong.... it sure would help with micro testing as the length wou would need to insert the cap is reduced. In fact I attribute this end contact problem to a recent failure I had with a 15g blob of plastic that did not fire and have considered trying the method I just outlined. that video on YouTube of the guy who made that real professional cap on detonators anonymous channel had an end made this way. Not enough free hours up my sleeve lately though.

Microtek - 15-12-2014 at 05:01

This is why caseless or semi caseless detonators are nice. If you use a cast energetic or a PBX for the base charge you can leave the end open, and therefore getting the most intimate contact possible between donor and receptor explosives.

markx - 16-12-2014 at 05:09

Quote: Originally posted by Microtek  
This is why caseless or semi caseless detonators are nice. If you use a cast energetic or a PBX for the base charge you can leave the end open, and therefore getting the most intimate contact possible between donor and receptor explosives.


True that, but cast base or pbx might be relatively hard to initiate, at least in the classical dimensions of an initiator charge. Depends of course what composition is used.
But perhaps the easiest way would be to leave the end of the base exposed....as in pressing the base charge into an open ended tube type containment. That way one can still retain structural integrity of the unit and have the added value of the exposed base charge tip. Just my 2 cents... :)

Microtek - 16-12-2014 at 06:26

You just have to have the lower part of the base charge cast (or bound). If you simply press the charge, you will lose too much structural stability.
If you are worried about initiability, use something like nipolit (RDX bound in NC or NC/NG in a solvent casting process), a PETN analogue, PTX-II or you can use a small percentage of an inert binder such as a PU based epoxy. In a base charge there is no need for mouldability (indeed, in a semi-caseless or caseless design it would be counter-productive), so an appropriate glue can be used in amounts of just 2-5 % to make a hard PBX, which is easily initiated.

markx - 17-12-2014 at 00:05

Quote: Originally posted by Microtek  
You just have to have the lower part of the base charge cast (or bound). If you simply press the charge, you will lose too much structural stability.
If you are worried about initiability, use something like nipolit (RDX bound in NC or NC/NG in a solvent casting process), a PETN analogue, PTX-II or you can use a small percentage of an inert binder such as a PU based epoxy. In a base charge there is no need for mouldability (indeed, in a semi-caseless or caseless design it would be counter-productive), so an appropriate glue can be used in amounts of just 2-5 % to make a hard PBX, which is easily initiated.


Yes, options are plentyful and limited mostly by the reach of our own imagination or lack of knowledge :)

Though I'm a bit worried about the critical diameter of PBX or melt cast bases with "classical" initiator dimensions (6-8mm). Depending on formulation this might become a limitation to success. Not saying that it will happen, just another aspect that must be accounted for when designing such a device. I've often ran into trouble when trying to initiate charges with limited dimensions and high density, either due to pressing, phlegmatisation additives or inert binders.

Turner - 17-12-2014 at 21:05

I have found the best option to be using basic plastic pen cases, the tubes can be cut to length, easily loaded and fused.

I have never had a failure in initiating a charge with these caps I made. People like to try and get clever and creative with detonators when I see no need to do so. There isn't much sense in using cast melt explosives or PBX's in the detonator itself. 500-1000mg of Pressed RDX, PETN etc. with 30-150mg of primary is all that's needed.

As seen here:




Here is a 17g TNT cast with the hole molded:



45g Picric Acid booster w/ same detonator:





A 60g ETN cast here detonated with the same detonator:



Decomposition of said ETN cast:






I've done quiet a few detonations but always stuck with the same style detonator, 700mg ETN and 200mg roughly SADS

markx - 17-12-2014 at 23:40
Quote:

People like to try and get clever and creative with detonators when I see no need to do so. There isn't much sense in using cast melt explosives or PBX's in the detonator itself. 500-1000mg of Pressed RDX, PETN etc. with 30-150mg of primary is all that's needed.


Well, it depends on what your goal is....if you need a simple and working solution that does nothing more than fulfilling its function, then there is no need to get more clever about it :)

On the other hand one might feel the need to explore the effects of a more complicated and untried system. Who knows, perhaps we might stumble on something interesting in the process.....

Microtek - 18-12-2014 at 03:59

I'm sure that your (Turner) detonators perform just fine with the type of demands that you place on them, but it seems that your charges are rather large, so it is not out of place to use a large detonator, possibly along with a booster. But if you're experimenting on the sub gram scale (main charge) then these solutions don't work well.

Hennig Brand - 18-12-2014 at 10:49

I have seen that cast TNT picture before. I think it was from a YouTube video. Seems to me the charge didn't detonate IIRC.

Turner - 18-12-2014 at 10:53

Yes, that one failed because I over pressed the ETN base charge in the cap and was insensitive to the SADS. I corrected this and they worked fine ever since.

Hennig Brand - 18-12-2014 at 19:19

Did you get the cast TNT to detonate? If so, what did you use for an initiator?
From what I have learned, having a good understanding of initiation is very important and it can be much harder to learn (less intuitive) than a lot of the other energetic materials topics.

Turner - 18-12-2014 at 19:57

No, the TNT was scattered around in small bits/pieces. I didn't really bother to pick the pieces up. When experiencing with the detonation of an explosive as insensitive as TNT I think you need to use larger amounts. Probably 30 grams at least for a cast charge just to meet critical diameter/critical mass. I had the intention of trying to detonate TNT again, but it is by far the most time consuming and tedious process to make the material and I never got around to it, might be a neat little project some time down the line. 17 grams was all the yield I got out of my synthesis because of a few mistakes I made.


By the way for anyone who is curious, here is the video of the AN/Al and picric acid booster detonating:

<iframe sandbox width="560" height="315" src="//www.youtube.com/embed/Orp9gb_uE3U" frameborder="0" allowfullscreen></iframe>


[Edited on 19-12-2014 by Turner]

Hennig Brand - 19-12-2014 at 06:13

Good to see you staying heart healthy by getting some cardio. :D

I don't want to get too far off topic, but I thought I would include the following jpg of a table taken from an old defense document (Powder and Explosives by A. G. Gorst). It provides some minimum mercury fulminate initiator charge weights for cast and pressed TNT and Picric Acid. As you know, granular TNT and picric acid are much easier to initiate than their cast forms. Very commonly, granular or crystalline TNT or picric acid was used as a booster to initiate cast TNT and cast picric acid.

BTW, did you check the melting point of your TNT? TNT even when of high purity is relatively insensitive to initiation.

TNT does take a bit of time to make, but after doing it a couple of times I find it fairly straightforward and with the right equipment (large flasks, etc) it could be made in large quantities relatively safely. It wouldn't take much longer to make a pound batch than it would to make a 15g batch.

TNT & Picric Acid - Influence of Physical Structure on Charge Sensitivity.jpg - 58kB


[Edited on 20-12-2014 by Hennig Brand]

ecos - 19-12-2014 at 11:58

What is wrong about syringe casing?
I found some pics for this but it doesn't look nice
i personally shape it in a better way
is there anything attractive about metal casing?

NeonPulse - 19-12-2014 at 15:55

They look pretty large. What is in them? The rubber plunge could be replaced making them a little more compact. And the confinement isn't going to be as strong as if they were made of Al.

markx - 22-12-2014 at 00:07

Quote: Originally posted by ecos  
What is wrong about syringe casing?
I found some pics for this but it doesn't look nice
i personally shape it in a better way
is there anything attractive about metal casing?



There is nothing intrinsically wrong with syringe casings...just one has to pick a suitable size and work out a neat and clean assembly and a "safe" process for it. For example insulin syringes would be of more appropriate dimesions.
The ones on the picture are quite horrible and I would stay well away from using or handling such devices. If one can not spare the time and effort to perform clean and reproducible work, then researching the field of energetics is not a suitable passtime.
Apart from unrivaled mechanical integrity in construction and handling there is not much more attractive in a metal confinement. In fact I would avoid it in amateur practice at all cost. The danger of shrapnel outweighs any possible advantages of metal casings for me. That's my personal opinion on the matter, but one has to make up its own mind about these choices.

magneet - 22-12-2014 at 14:41

An old photo:

4 mm dia Transparent straw casing, with direct contact HE plug, handpressed.

12% inert PETN PBX ribbon on 3 mm Al, covered in sand.
post-51-0-99777600-1344546075.png - 2.9MB

ecos - 23-12-2014 at 13:19

Quote: Originally posted by markx  
Quote: Originally posted by ecos  
What is wrong about syringe casing?
I found some pics for this but it doesn't look nice
i personally shape it in a better way
is there anything attractive about metal casing?



There is nothing intrinsically wrong with syringe casings...just one has to pick a suitable size and work out a neat and clean assembly and a "safe" process for it. For example insulin syringes would be of more appropriate dimesions.
The ones on the picture are quite horrible and I would stay well away from using or handling such devices. If one can not spare the time and effort to perform clean and reproducible work, then researching the field of energetics is not a suitable passtime.
Apart from unrivaled mechanical integrity in construction and handling there is not much more attractive in a metal confinement. In fact I would avoid it in amateur practice at all cost. The danger of shrapnel outweighs any possible advantages of metal casings for me. That's my personal opinion on the matter, but one has to make up its own mind about these choices.

I agree the picture is horrible. I just got it from internet.
i also use insulin syringes 1mL. I close the narrow part using small fire then fill from other part.