Baluncore said:
Are you trying to produce an open or a closed cell foam ?
What do you want as the filling of the voids ?
An iron melt will behave like aluminium to magnetic fields. The curie point will not prevent shielding because as a conductor it will take time for the magnetic field to penetrate. Use an estimate of about 5 metre per second for the magnetic penetration rate, (skin effect). Since hot iron is more resistive than cold, (proportional to absolute temp), it may penetrate faster.
The rotating disk used in an energy meter is made from aluminium, you could induce the same motion in molten metal by providing the necessary phasing of external magnetic fields.
If you implanted metal, ceramic or salt spheres with a gun, deep into the melt, you might be able to control their final positions, a bit like a 3D printer. Iron spheres would remain magnetic for a short time, so long as their kinetic energy on impact did not heat them above their curie point.
It might be possible to implant rods using the same process. If the rod then melted and produced a line of liquid drops or gas bubbles you would get a fondue. With an open cell foam you could exchange the void filling later.
Volcanic rock often has bubbles in it. If you introduce a gas under pressure that will dissolve in a high pressure melt then, when you release the pressure, you will get a foam like pumice stone.
Hydrogen and nitrogen will effect the properties of the metal. Argon would make an interesting bubble in iron if it could be dispersed before decompression. The introduction of something that released oxygen would produce CO2 bubbles in a carbon steel melt.
Hi, Baluncore. Thanks for your response!
I would like to make a closed cell foam. Anything that has density significantly less than that of steel would work as a fillant of the voids. The price for that material should be reasonable.
Sorry. I couldn't get what exactly you mean in the second paragraph. Could you please explain more about that? Isn't the Skin Effect closely connected to an AC current that produces a changing magnetic field? And we would like to use a constant magnetic field for taking those spheres into the melt (or maybe we can't use a constant field? Then why?) We probably shouldn't use inductive heating for creating the melt since eddy currents will be of the same trouble that you describe in the second paragraph. Then resistive heating?
I didn't know that the disk is made of aluminum. Thanks for the info. Don't we need to get some current going through the plunged spheres in order to get the same motion as in an energy meter?
Do you think it would be possible to use a gun for creating a relatively uniform distribution of voids without structural abnormalities (e.g. 2 voids in 10 cm^3 in one part vs. 10 voids in 10 cm^3 in another part of the resultant foam)? Wouldn't it also impose a restriction of the depth of the melt to which the projectiles would penetrate? (Or maybe we could adjust that by changing the force at which the projectile is "thrown" toward the melt? Then again, with a high force wouldn't we create a mess by destroying a pattern of the layers of voids below as we go up with new spheres?) Viscosity is something very important to consider in that technique borrowed from 3d printers (the melt is very viscous, so often agents that reduce it are added in making metallic foams).
Mentioning gas bubbles you basically described several techniques of creating metallic foams (like gasar process). Their main disadvantage is the lack of uniform distribution. Research on metallic foams is going now in the direction of finding a cheap way of getting uniform distribution (surely without losing one of the main qualities: efficient energy absorbtion). Volcanic rocks do have bubbles in them but there isn't a strict pattern, so you can't rely on such a material.
This is my bad, I should have said in the very beginning that distribution of the voids should follow some pattern without high deviations (otherwise the material becomes unreliable, right?). Syntactic Steel/Al Foams are leading in this field so far, and they are made with alumina hollow spheres.
There are some cool applications. You can find them here http://www.ergaerospace.com/project-gallery.htm That includes Virgin Galactic's Spaceplanes and the Space Shuttle (R.I.P.) I'm new here and I hope it isn't against the rules of this forum to post a link.
Thanks for your ideas, Baluncore!
