Sciencemadness Discussion Board

Blasting cap ignition mix

mabuse_ - 5-12-2010 at 11:08


maybe you can give me some advice.

I've just tried out my latest lead azide/PETN Blasting Cap.

Lead Azide seems to ignite with Viscofuse, but I find it more reliable and safer to manufacture with some ignition mix on top.
When I mount the endplug with the fuse I don't directly squeeze or rub the lead azide, only the ignition mix.

I tried Blackpowder, "green mix" with 5% Silicone and it worked fine.

Do you know what they use in commercial caps?

It should be possible to store the cap for some time.

hissingnoise - 5-12-2010 at 11:36

Styphnic acid (trinitroresorcinol) is used in commercial caps!
A layer of this material is pressed onto the LA in the cap.

quicksilver - 5-12-2010 at 11:58

I believe that it's lead styphnate that is one of the flame sensitizers for lead azide. Not to get into to much practical use of the chemistry but lead azide when quite well compacted is slightly less sensitive to a flame spit so that in manufacturing there was often a "layered" technique and a "mixed" technique to the production of fuse-caps.

One of the more interesting issues chemically in the azides is their sensitivity to various stimulus: lost of good material on that subject.

Rosco Bodine - 5-12-2010 at 13:40

There are also picrate based primers that are good. Here's three.

mabuse_ - 6-12-2010 at 13:53

Thanks for your replies.

Do i really need an ignition mix that undergoes DDT?
I was under the impression that lead azide can do this alone very well and without any sacrifice in performance.
What improvement can i expect from using a picrate oder styphnate mix?

I mean, the lead azide seems to detonate without any hesitation when it comes in contact with burning blackpowder, i did several tests without any failure.

The KNO3 is slightly hygroscopic, but if the cap is stored dry and sealed with epoxy resin that should not be a problem.
I might swap it for KClO4...

quicksilver - 7-12-2010 at 07:29

There are MANY very fine techniques for long lasting sealants for fuse caps. However the specifics of the Forum is to keep the discussion on the science-level of energetic rather than the practical.
In industrial production a thick seal of NC lacquer was typically used (in fuse-cap production as it lasted a long time, has pliability, was air & moisture tight and was exceedingly reactive to flame). Today there is perhaps one manufacturer that mfg true fuse caps. The shift to Nonel has made that agenda obsolete. The issues also afforded a measure of safety as well as profit. Although Nonel functions relatively the same as a fuse there are adapters on each cap and on the end of the tubing of the Nonel.
This also results in a safety agenda and a profit margin even higher than it had been after major legislation was past to serialize each cap with a great deal of information (& the bookkeeping to match) which had the effect of raising the cost well over 600%. (E.E.T. bi-monthly journal).


As an after thought there are electronic components in some caps today that allow for timing alterations, near guarantees of functionality, the elimination of bride-wires and a "safety shut off" component. This brings the cost of a single cap to the $20 mark and higher! Whereas in the 1930's, common fuse caps sold for less than $1 or $2 per 100 in a carton. The "high-end" caps are occasionally sold as one half to one dozen per box as modern techniques allow for their limited use; which becomes a profound safety issue.
However, remember that fulminate fuse caps (depending upon the temperature conditions of the magazine and other factors affecting fulminate had a shelf life of generally less than a year). Today the 20yr mark is not unheard of.

[Edited on 7-12-2010 by quicksilver]

pjig - 7-12-2010 at 18:07

So would it be safe to say ,that LA could be used with out the LS as a top layer... and go just for a hot NC+ metal powder "sealant" , as your ignition mix...? LS being a added =sensitivity factor to static and other mechanical stimulation dangers V.S. just having a Prime " sealant covering the LA alone. I like the latter better from that stand point.

[Edited on 8-12-2010 by pjig]

quicksilver - 8-12-2010 at 07:03

We need always understand that NC and metal powders may have an unfortunate agenda to "cake" and form a layer of the metal powder - so I would advise to either take it easy with the metal powders OR use a larger mesh size: but I believe that's right on the money.
Additionally I would add that silver azide is today's standard as the lessened sensitivity to static & it's basic strength makes it worth the expense.

However it's (finely divided Al powder) used as a "dry lubricant" also used to drastically reduce friction in in the "packing" of the train of materials in manufacturing process & extremely fine powder does have a place in the process.

[Edited on 8-12-2010 by quicksilver]

pjig - 8-12-2010 at 20:33

Would it be adventitious to use a NC lacquer and then dust lightly with a Magnal or fine aluminium , then mixed very thin with acetone ,finally to be dripped into the cap ?

Now would bright flake be the choice here for aluminium! It has a greasy coating that may help aid in the lubrication process. It is cheap, unlike dark aluminium. Not an easy task to remove that bright stuff off your hands or cloths :o..

[Edited on 9-12-2010 by pjig]

quicksilver - 9-12-2010 at 06:48

I believe that would function appropriately.
Actual design complexities and the science behind them is found in USBoM papers and the text "Detonators" by Hall & Howell (if it's still in print; it may be one of the last places where USBoM collections were published.