General Question

XOIIO's avatar

Curious about the old fashioned movie style of detonating explosives.

Asked by XOIIO (16868 points ) March 5th, 2014

Hey all, I’m sure we all have seen the old fashioned way movies depict blowing up TNT, with a box and a T coming out the top, push it down, and you have your explosion, I’m wondering what that is actually called, and I’d like to learn more about how it actually worked, I’m guessing it maybe had a peizo electric material in the bottom to generate an electric charge, or perhaps a mechanism similar to the magneto in old phones.

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9 Answers

Symbeline's avatar

Randomly looked around, Wiki is being shit as per usual, so I dug deeper.

Here’s a message board where some people explain this. So it’s called a plunger.

I am not confirming anything on the accuracy of what is said there. Made for some inneressin’ readin’ though.

Tropical_Willie's avatar

Don’t blow yourself up!

And answer the door bell if it is the AFT guys.

XOIIO's avatar

ah, cool, I was right, it does use a magneto to make the electricity needed.

Don’t know why I didn’t think of the word plunger lol

kritiper's avatar

It’s called a blasting machine. My DuPont Blaster’s Handbook (copyright 1930) shows one, a Du Pont No. 5 G. M. (push down) Blasting Machine. Developed by General Motors. It generates a spark to detonate an electrical blasting cap. Would guess that it indeed had a gizmo like a magneto. I’ve listened to the things and it sounds as though the plunger drives a flywheel of sorts to generate the electrical charge. Among it’s features are: “a two-point clutch which enables the current to be sent out at it’s peak; a laminated armature and solid core field for building up the maximum current; a one micro farad condenser to store up the current until the moment of discharge; and a new eight point breaker of unique design which utilizes the current hetetofore in evidence as a large spark at the completion of the stroke. The mechanical improvements consist of the field windings being placed so as to increase the efficiency of the machine; ball bearings on the armature shaft; and a thrust bearing for the rack bar in direct line of thrust instead of offset as formally.” It’s working parts consist of: rack bar, contact spring (which, when struck by the bottom of the descending rack bar, breaks the contact between two small platinum contacts, one on the upper surface of the contact spring and the other on the underside of the bridge, and in this way throws the entire current through the outside circuit, that is, leading wire, electric blasting caps, and connecting wire); field magnets, revolving armature, rack bar handle.
FYI You can’t set off dynamite with a gun, fire, or a fire cracker. You need a blasting cap or another explosion. Nitro glycerin can be set off with a small jolt, black powder can be set off with a spark. Dynamite is SO much safer!

XOIIO's avatar

@kritiper Yup, most explosives (especially one of the most used these days, C4) need both the extreme heat and shockwave produced by a blasting cap. I believe the same is true for industrial explosives like ANFO which is used for mining.

kritiper's avatar

@XOIIO As it was explained to me, it isn’t the heat but the sudden shock that is needed to set it off. In excess of 75 lbs per sq.” I’m sure ANFO is the same. I am no expert in explosives, though… My grandfather used explosives in his mining operations.

XOIIO's avatar

@kritiper I’d have to look for the source but I’ve always heard it needs both, heck you can shoot C4 and it won’t go off, mythbusters tested that.

kritiper's avatar

@XOIIO You can burn it too and it won’t go off. C4 makes a great emergency cooking fuel! I suppose extreme heat is a given because if you compressed it fast enough, it would naturally get hot.

XOIIO's avatar

@kritiper yup, I always have some c4 in my survival kit, lol

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