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Quarter shrinker shrapnel direction

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MRMILSTAR

Wed Mar 13 2019, 09:13PM

Registered Member #62119 Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136

Does anyone know the primary direction that the exploded wire fragments from a quarter shrink move? Do the fragments move mostly outward away from the coil, perpendicular to the coil axis? Or do they mostly move laterally in the direction of the winding form? Or is there no preferred direction? This information will be helpful in the design of my blast cage.

Signification

Fri Mar 15 2019, 07:04AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

Assume it flies in EVERY direction! I buried my wrapped quarter DEEPLY in the sand of a giant hologram vibration-isolation table (4' x 8')...couple tons. I inserted it in the sand via a into a hole cut in a 4' x 4' x 3/4" plywood sheet and covered the hole with a GIANT HEAVY dictionary. The blast threw shrapnel EVERYWHERE! but is was contained. The pulsed field also shrunk and peeled the coil into 100's of small lengths of razer-sharp projectiles, some of which came out of the sand and buried themselves into the book and plywood. When I finally found the quarter, after a while of digging, I lifted it with my bloody hand, which then became bloody AND burned. Way to much power!

If you are asking this question, then start with much lower Joule energy than you think.

Uspring

Fri Mar 15 2019, 11:18AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

Parallel wires carrying current in the same direction will attract each other. Adjacent wires in the coil will do that and cause the coil to be compressed along its axis. If that's violent enough, top windings will smash lower windings or shoot through and come out at the bottom. And the other way around.
The wires will also be affected by the other side of the coil, which carries the current in the opposite direction. So there is also an outward force perpendicular to the axis. To sum up, the blast will go everywhere.

MRMILSTAR

Fri Mar 15 2019, 02:50PM

Registered Member #62119 Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136

I will assume then that the fragments will exit in all directions and design accordingly.

I am also wondering how tight to seal my blast box. I plan on dimensions of 12" x 12" x 12". The floor will be made from 1" thick G10. The sides and top will be made from 1/2" G10. The corners will be reinforced with angle iron. Sand will cover the bottom. Does this seem adequate?

Another question I have is how tight to seal the blast box. I know the fragments are very high speed but have very low mass. I know how to contain those. My concern is the thermal expansion of the air inside the box. I am thinking that I cannot completely seal this box because of the air expansion or it may blow apart. I am thinking of cutting some holes in the top with baffles to allow the expanded air to safely exit the box without blowing it apart. The baffles would prevent any fragments from leaving the box. Any thoughts?

hen918

Fri Mar 15 2019, 08:18PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

I think the baffles would also contain the air during the expansion (in the short term the air isn't gonna make its way past them) so don't put too much effort into making them, some small holes with a single baffle to stop debris shooting out of them should do. I hope you have a powerful welder!

MRMILSTAR

Sat Mar 16 2019, 12:06AM

Registered Member #62119 Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136

Powerful welder? For what? I plan on mostly using G10.

Signification

Sun Mar 17 2019, 02:37AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

G10 may work, I would trust metal with a VERY thick window if needed for observing BEFORE & AFTER. Certainly NOT up close DURING, the blast. Just a 10T single layer of 10AWG magnet wire works. I saw a youtube video with a dedicated quarter shrinker design that appeared to take up an entire room!! NOT necessary!! They used 12 or even 14 AWG wire-can't remember. Gave accurate specs too. There was an audience.

Patrick

Sun Mar 17 2019, 05:39AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

this sounds like an excellent anti-personnel weapon system.

klugesmith

Fri Mar 22 2019, 06:44AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

MRMILSTAR wrote ...

My concern is the thermal expansion of the air inside the box. I am thinking that I cannot completely seal this box because of the air expansion or it may blow apart. ... Any thoughts?

As said before, not a whole lot of "blast" energy relative to total energy. Signification and Hackerbot report weighted lids being heaved up, not launched!

I bet most of the electrical energy goes into plastic deformation of the coil and tearing the work coil to bits. For the latter, could get a ballpark answer from copper wire tensile-test charts, or machining guidelines (spindle power x time to reduce that mass of copper to tiny chips).
Most of the remaining energy goes into heating the copper, and kinetic energy of the fragments.
I guess there's some immediate hot-gas energy from the brief electrical arcing. Then as fragments cool, whatever heat doesn't go into the solid materials they are touching will go into the air.

A super conservative analysis would figure 100% of the initial stored energy heats the air ( I bet the real percentage is closer to 10% ).
Anyway, your 12 inch cube holds about 34 grams of air, with thermal mass (at constant volume) of about 25 joules per K. So average temperature would go up about 40 K per kJ. 2.5 kJ would give a temperature rise of about 100 Â°C, and according to Boyle that would increase the pressure by about 1/3 of an atmosphere. I'll believe it when I see it.

Signification

Fri Mar 22 2019, 07:29AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

Here is that lab:

edit:
Well, This is not the video I thought it was, but I think that tall shrinking machine is the same one.

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