Is "pressing" explosives necessary?

DXM Dave · #1 (**permalink**) 10-30-2009, 10:12 AM

I believe I've read some literature about the need to press the explosives before detonation (I'm thinking HMTD or acetone peroxide that sorta thing). Is pressing really necessary or does it just increase the detonation velocity?

Timm · #2 (**permalink**) 10-30-2009, 04:29 PM

With sensitive stuff, like most primaries, pressing consolidates the explosive and makes it less sensitive to shock by preventing its free movement.
However some stuff needs pressed to a certain density before it will perform at its potential, e.g. chlorate and wax mixtures or similar need to be squished down to about 1.33 grams/cc for optimum velocity.
A press is a pretty cool thing, you can do some crazy shit with one. And you need one to make black powder, so you might as well put it on the list.

When i first started making caps, i thought i would have to press each one to get the primary down to a more suitable density.. however when i did the math, to get 3000 pounds of pressure on the fulminate in the aluminum tubing i was using required something like 37 pounds on the wooden plunger thing.

ninefingers · #3 (**permalink**) 11-06-2009, 01:08 PM

Plus, with fulminate, there is "dead pressed"--a point where it won't go off readily anymore. That's one reason it isn't used anymore.

Timm · #4 (**permalink**) 11-07-2009, 02:16 AM

Yeah, but its like at 9 to 12,000 psi i think when its starts to get finicky, and i thought 20 to 30,000 for a true dead press. Not gonna happen with hand pressure, no matter how small the cross-section. It's lost popularity beacuse its not quite as storage stable as lead azide, (esp. at 100+ deg F, but not a problem here!) nor does it have the same initiatory power, but its way easy to improvise, and is reliable. Hell, they used it almost exclusively for 100 plus years, can't be that bad..

ninefingers · #5 (**permalink**) 11-09-2009, 02:18 PM

Quote:

Originally Posted by Timm

Yall the cross-section. It's lost popularity beacuse its not quite as storage stable as lead azide, (esp. at 100+ deg F, but not a problem here!)s

Oh, by the way, with the 106 deg.weeks here, chlorate/Vaseline plastics and other things dor erode quickly. I have a small 1 cu ft. 'reefer in the garage for such things. My HNO3 goes bad in less than a year if not cooled.

Plus, Merc. Fulm. is easier than lead styphnate/azide, of course. That stupid Resorcinol, a tree sap used in most glues, is expensive. My "Honey Uncle"--a ret'd. Chem teacher that cleaned up after drug busts and got a lot of "freebies"--gave me a bottle. I can't find Sodium Amide. It can be made.

Timm · #6 (**permalink**) 11-09-2009, 07:43 PM

Yeah me too, 80/20 fulminate/chlorate atop PETN scavenged from det cord. Or ETN, with or without a slpash of nitroglycol added. It probably wasn't too hard to find a fulminate cap in the sixties, but i can't be sure cause i was never there.

And yeah, Pounds per Square Inch add up quick when the thing you're pushin on is only.19" in diameter.. Do the math which i forget the exact particulars of for area of a circle, multiply to get an inch, then you have your multiplier number that you get psi from pounds of pressure on the plunger..or something.

ninefingers · #7 (**permalink**) 11-10-2009, 01:35 PM

Yeah, what I figured...just wanted to know your plunger size.

I found some 'dope on F/M pressing. Also, a lot on Primaries and secondaries pressed for greater effect. "The Chemistry of Powder and Explosives".